Inconsistency with cmp_instance and typedispatch because of binary sort algorithm

[kessido]

Basically, typedispatch assume that the type in funcs are ordered in a topological sort, but this is not true as the key comparison is not defined well under this.

stupid example (edited, now it is less stupid :P ):

>>> from fastcore.dispatch import *
>>> 
>>> class A: pass
... 
>>> class B(A): pass
... 
>>> @typedispatch
... def f(a:A): print('A')
... 
>>> @typedispatch
... def f(x:int): pass
... 
>>> @typedispatch
... def f(x:tuple): pass
... 
>>> @typedispatch
... def f(b:B): print('B')
... 
>>> @typedispatch
... def f(x:list): pass
... 
>>> f(B()) 
A
>>> print(f)
(list,object) -> f
(tuple,object) -> f
(A,object) -> f
(int,object) -> f
(B,object) -> f

doing insertion sort variation with the key comparison at hand will solve the issue I believe. I can implement this quickly but would love hearing your opinion first.

Ido

[jph00]

I'd love to see your approach as a PR - honestly, I didn't put that much time into thinking about the sort, and just kinda used the first thing I tried because it passed my tests! I'm glad you've taken the time to think through it more carefully. A test showing where the existing approach breaks would be very useful to include in the PR.