mypy

c61bce4e - [mypyc] Fixing __init__ for classes with @attr.s(slots=True). (#18447)

[mypyc] Fixing __init__ for classes with @attr.s(slots=True). (#18447) Fixes mypyc/mypyc#1079. `@attr.s` generates a `__init__` function which was getting lost in `CPyDataclass_SleightOfHand`. This change copies the generated `__init__` function and a couple of others ones to maintain consistency with CPython.