[red-knot] Port type inference tests to new test framework (#13719)

## Summary

Porting infer tests to new markdown tests framework.

Link to the corresponding issue: #13696

---------

Co-authored-by: Carl Meyer <[email protected]>

crates/red_knot_python_semantic/resources/mdtest/assignment/annotations.md

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+# Assignment with annotations
+
+## Annotation only transparent to local inference
+
+```py
+x = 1
+x: int
+y = x
+
+reveal_type(y)  # revealed: Literal[1]
+```
+
+## Violates own annotation
+
+```py
+x: int = 'foo' # error: [invalid-assignment] "Object of type `Literal["foo"]` is not assignable to `int`"
+
+```
+
+## Violates previous annotation
+
+```py
+x: int
+x = 'foo'  # error: [invalid-assignment] "Object of type `Literal["foo"]` is not assignable to `int`"
+```

crates/red_knot_python_semantic/resources/mdtest/assignment/multi_target.md

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+# Multi-target assignment
+
+## Basic
+
+```py
+x = y = 1
+reveal_type(x)  # revealed: Literal[1]
+reveal_type(y)  # revealed: Literal[1]
+```

crates/red_knot_python_semantic/resources/mdtest/assignment/unbound.md

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+# Unbound
+
+## Maybe unbound
+
+```py
+if flag:
+    y = 3
+x = y
+reveal_type(x)  # revealed: Unbound | Literal[3]
+```
+
+## Unbound
+
+```py
+x = foo; foo = 1
+reveal_type(x)  # revealed: Unbound
+```
+
+## Unbound class variable
+
+Class variables can reference global variables unless overridden within the class scope.
+
+```py
+x = 1
+class C:
+    y = x
+    if flag:
+        x = 2
+
+reveal_type(C.x) # revealed: Unbound | Literal[2]
+reveal_type(C.y) # revealed: Literal[1]
+```

crates/red_knot_python_semantic/resources/mdtest/assignment/walrus.md

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+# Walrus operator
+
+## Basic
+
+```py
+x = (y := 1) + 1
+reveal_type(x)  # revealed: Literal[2]
+reveal_type(y)  # revealed: Literal[1]
+```
+
+## Walrus self-addition
+
+```py
+x = 0
+(x := x + 1)
+reveal_type(x)  # revealed: Literal[1]
+```

crates/red_knot_python_semantic/resources/mdtest/attributes.md

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+# Class attributes
+
+## Union of attributes
+
+```py
+if flag:
+    class C:
+        x = 1
+else:
+    class C:
+        x = 2
+
+y = C.x
+reveal_type(y)  # revealed: Literal[1, 2]
+```

crates/red_knot_python_semantic/resources/mdtest/binary/integers.md

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+## Binary operations on integers
+
+## Basic Arithmetic
+
+```py
+a = 2 + 1
+b = a - 4
+c = a * b
+d = c // 3
+e = c / 3
+f = 5 % 3
+
+reveal_type(a)  # revealed: Literal[3]
+reveal_type(b)  # revealed: Literal[-1]
+reveal_type(c)  # revealed: Literal[-3]
+reveal_type(d)  # revealed: Literal[-1]
+reveal_type(e)  # revealed: float
+reveal_type(f)  # revealed: Literal[2]
+```
+
+## Division by Zero
+
+```py
+# TODO: `a` should be `int` and `e` should be `float` once we support inference.
+a = 1 / 0  # error: "Cannot divide object of type `Literal[1]` by zero"
+b = 2 // 0  # error: "Cannot floor divide object of type `Literal[2]` by zero"
+c = 3 % 0  # error: "Cannot reduce object of type `Literal[3]` modulo zero"
+d = int() / 0  # error: "Cannot divide object of type `int` by zero"
+e = 1.0 / 0  # error: "Cannot divide object of type `float` by zero"
+
+reveal_type(a)  # revealed: float
+reveal_type(b)  # revealed: int
+reveal_type(c)  # revealed: int
+reveal_type(d)  # revealed: @Todo
+reveal_type(e)  # revealed: @Todo
+```

crates/red_knot_python_semantic/resources/mdtest/call/callable_instance.md

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+# Callable instance
+
+## Dunder call
+
+```py
+class Multiplier:
+    def __init__(self, factor: float):
+        self.factor = factor
+
+    def __call__(self, number: float) -> float:
+        return number * self.factor
+
+a = Multiplier(2.0)(3.0)
+
+class Unit: ...
+
+b = Unit()(3.0) # error: "Object of type `Unit` is not callable"
+
+reveal_type(a) # revealed: float
+reveal_type(b) # revealed: Unknown
+```

crates/red_knot_python_semantic/resources/mdtest/call/constructor.md

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+# Constructor
+
+```py
+class Foo: ...
+
+x = Foo()
+reveal_type(x)  # revealed: Foo
+```

crates/red_knot_python_semantic/resources/mdtest/call/function.md

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+# Call expression
+
+## Simple
+
+```py
+def get_int() -> int:
+    return 42
+
+x = get_int()
+reveal_type(x)  # revealed: int
+```
+
+## Async
+
+```py
+async def get_int_async() -> int:
+    return 42
+
+x = get_int_async()
+
+# TODO: we don't yet support `types.CoroutineType`, should be generic `Coroutine[Any, Any, int]`
+reveal_type(x)  # revealed: @Todo
+```
+
+## Decorated
+
+```py
+from typing import Callable
+
+def foo() -> int:
+    return 42
+
+def decorator(func) -> Callable[[], int]:
+    return foo
+
+@decorator
+def bar() -> str:
+    return 'bar'
+
+x = bar()
+
+# TODO: should reveal `int`, as the decorator replaces `bar` with `foo`
+reveal_type(x)  # revealed: @Todo
+```
+
+## Invalid callable
+
+```py
+nonsense = 123
+x = nonsense()  # error: "Object of type `Literal[123]` is not callable"
+```

crates/red_knot_python_semantic/resources/mdtest/call/union.md

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+# Unions in calls
+
+## Union of return types
+
+```py
+if flag:
+    def f() -> int:
+        return 1
+else:
+    def f() -> str:
+        return 'foo'
+
+x = f()
+reveal_type(x)  # revealed: int | str
+```
+
+## Calling with an unknown union
+
+```py
+from nonexistent import f # error: [unresolved-import] "Cannot resolve import `nonexistent`"
+
+if flag:
+    def f() -> int:
+        return 1
+
+x = f()
+reveal_type(x)  # revealed: Unknown | int
+```
+
+## Non-callable elements in a union
+
+Calling a union with a non-callable element should emit a diagnostic.
+
+```py
+if flag:
+    f = 1
+else:
+    def f() -> int:
+        return 1
+
+x = f()  # error: "Object of type `Literal[1] | Literal[f]` is not callable (due to union element `Literal[1]`)"
+reveal_type(x)  # revealed: Unknown | int
+```
+
+## Multiple non-callable elements in a union
+
+Calling a union with multiple non-callable elements should mention all of them in the diagnostic.
+
+```py
+if flag:
+    f = 1
+elif flag2:
+    f = 'foo'
+else:
+    def f() -> int:
+        return 1
+
+x = f()  # error: "Object of type `Literal[1] | Literal["foo"] | Literal[f]` is not callable (due to union elements Literal[1], Literal["foo"])"
+reveal_type(x)  # revealed: Unknown | int
+```
+
+## All non-callable union elements
+
+Calling a union with no callable elements can emit a simpler diagnostic.
+
+```py
+if flag:
+    f = 1
+else:
+    f = 'foo'
+
+x = f()  # error: "Object of type `Literal[1] | Literal["foo"]` is not callable"
+reveal_type(x)  # revealed: Unknown
+```

crates/red_knot_python_semantic/resources/mdtest/comparison/integers.md

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+# Comparing integers
+
+## Integer literals
+
+```py
+a = 1 == 1 == True
+b = 1 == 1 == 2 == 4
+c = False < True <= 2 < 3 != 6
+d = 1 < 1
+e = 1 > 1
+f = 1 is 1
+g = 1 is not 1
+h = 1 is 2
+i = 1 is not 7
+j = 1 <= "" and 0 < 1
+
+reveal_type(a)  # revealed: Literal[True]
+reveal_type(b)  # revealed: Literal[False]
+reveal_type(c)  # revealed: Literal[True]
+reveal_type(d)  # revealed: Literal[False]
+reveal_type(e)  # revealed: Literal[False]
+reveal_type(f)  # revealed: bool
+reveal_type(g)  # revealed: bool
+reveal_type(h)  # revealed: Literal[False]
+reveal_type(i)  # revealed: Literal[True]
+reveal_type(j)  # revealed: @Todo | Literal[True]
+```
+
+## Integer instance
+
+```py
+# TODO: implement lookup of `__eq__` on typeshed `int` stub.
+def int_instance() -> int: ...
+a = 1 == int_instance()
+b = 9 < int_instance()
+c = int_instance() < int_instance()
+
+reveal_type(a)  # revealed: @Todo
+reveal_type(b)  # revealed: bool
+reveal_type(c)  # revealed: bool
+```

crates/red_knot_python_semantic/resources/mdtest/comparison/non_boolean_returns.md

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+# Non boolean returns
+
+Walking through examples:
+
+- `a = A() < B() < C()`
+
+    1. `A() < B() and B() < C()` - split in N comparison
+    1. `A()` and `B()`              - evaluate outcome types
+    1. `bool` and `bool`            - evaluate truthiness
+    1. `A | B`                    - union of "first true" types
+
+- `b = 0 < 1 < A() < 3`
+
+    1. `0 < 1 and 1 < A() and A() < 3` - split in N comparison
+    1. `True` and `bool` and `A` - evaluate outcome types
+    1. `True` and `bool` and `bool` - evaluate truthiness
+    1. `bool | A` - union of "true" types
+
+- `c = 10 < 0 < A() < B() < C()` short-circuit to False
+
+```py
+from __future__ import annotations
+class A:
+    def __lt__(self, other) -> A: ...
+class B:
+    def __lt__(self, other) -> B: ...
+class C:
+    def __lt__(self, other) -> C: ...
+
+a = A() < B() < C()
+b = 0 < 1 < A() < 3
+c = 10 < 0 < A() < B() < C()
+
+reveal_type(a)  # revealed: A | B
+reveal_type(b)  # revealed: bool | A
+reveal_type(c)  # revealed: Literal[False]
+```