`list.sort()` fails to detect type issue

2.2 Regression with placeholder types in a TypeVar

`!= (None, None)` Narrowing only in else branch

Errors are unhelpful when variable type context disagrees with generic-involved dunder expression result

mypyc assertion error when generating `__ne__` from inherited `__eq__` in package import cycle

2.1 changelog is incorrect

redefinition-new does not apply type narrowing on cast-like function calls

mypy reports false-positive [exhaustive-match] error when there is an unreachable match

[Regression 1.19.1 -> 1.20.0] `value in container` based narrowing causes false negatives.

Do not require ast_serialize to avoid transitive dependency on Rust