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## Summary

This issue fixes the removal of empty lines between a leading comment and the previous statement:

```python
a  = 20

# leading comment
b = 10
```

Ruff removed the empty line between `a` and `b` because:
* The leading comments formatting does not preserve leading newlines (to avoid adding new lines at the top of a body)
* The `JoinNodesBuilder` counted the lines before `b`, which is 1 -> Doesn't insert a new line

This is fixed by changing the `JoinNodesBuilder` to count the lines instead *after* the last node. This correctly gives 1, and the `# leading comment` will insert the empty lines between any other leading comment or the node.



## Test Plan

I added a new test for empty lines.

…#4822)

Co-authored-by: Micha Reiser <[email protected]>

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## Summary

This PR replaces the `verbatim_text` builder with a `not_yet_implemented` builder that emits `NOT_YET_IMPLEMENTED_<NodeKind>` for not yet implemented nodes. 

The motivation for this change is that partially formatting compound statements can result in incorrectly indented code, which is a syntax error:

```python
def func_no_args():
  a; b; c
  if True: raise RuntimeError
  if False: ...
  for i in range(10):
    print(i)
    continue
```

Get's reformatted to

```python
def func_no_args():
    a; b; c
    if True: raise RuntimeError
    if False: ...
    for i in range(10):
    print(i)
    continue
```

because our formatter does not yet support `for` statements and just inserts the text from the source. 

## Downsides

Using an identifier will not work in all situations. For example, an identifier is invalid in an `Arguments ` position. That's why I kept `verbatim_text` around and e.g. use it in the `Arguments` formatting logic where incorrect indentations are impossible (to my knowledge). Meaning, `verbatim_text` we can opt in to `verbatim_text` when we want to iterate quickly on nodes that we don't want to provide a full implementation yet and using an identifier would be invalid. 

## Upsides

Running this on main discovered stability issues with the newline handling that were previously "hidden" because of the verbatim formatting. I guess that's an upside :)

## Test Plan

None?

* Use taiki-e/install-action to install cargo fuzz

The cargo fuzz run seems to sometimes fail for unclear reasons (https://github.com/charliermarsh/ruff/actions/runs/5200348677/jobs/9379742606?pr=4900). I hope that this might fix it. I'll push more commits to this PR to check the caching behaviour.

* Trigger CI with cache

* Change cache

* Actually use caching

* Undo cargo update

* cargo update fuzzer

* Revert rust changes

)