Do not use dictionary in CallableType

[ilevkivskyi]

This is mypyc-specific optimization: dict creation is quite slow, so we should not create a dict in the CallableType constructor. Instead, I store the required info on the relevant FuncDef object (and restore the link to definition in fixup.py). Quite surprisingly, this gives 2% speedup on my desktop.

[ilevkivskyi]

Oh, hm, this uncovers an inconsistency in how we format constructors, depending on whether they are decorated or not. IMO

def [T] list(self) -> list[T]

looks better than

def [T] __init__(self) -> list[T]

I will see how many tests needs updating to converge on this option, and if not too many, I am going to do it in this PR.

[ilevkivskyi]

Yeah, no, 15 tests need to be updated, this will also probably cause some noisy mypy_primer, so better to do in a separate PR. (Also maybe others have a different idea on which way looks better)

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

pydantic (https://github.com/pydantic/pydantic)
- pydantic/v1/validators.py:615: note:     def NamedTuple(self, str, Iterable[tuple[str, Any]], /) -> NamedTupleT
+ pydantic/v1/validators.py:615: note:     def __init__(self, str, Iterable[tuple[str, Any]], /) -> NamedTupleT
- pydantic/v1/validators.py:615: note:     def NamedTuple(self, str, None = ..., /, **kwargs: Any) -> NamedTupleT
+ pydantic/v1/validators.py:615: note:     def __init__(self, str, None = ..., /, **kwargs: Any) -> NamedTupleT