TYP: added missing __init__ in pandas/core/methods

[twoertwein]

See microsoft/pyright#4544 (comment)

Ruff's INP001 could have caught this. Could enable it if the following are ignored:

ci/fix_wheels.py:1:1: INP001 File ci/fix_wheels.py is part of an implicit namespace package. Add an __init__.py.
ci/test_wheels.py:1:1: INP001 File ci/test_wheels.py is part of an implicit namespace package. Add an __init__.py.
doc/make.py:1:1: INP001 File doc/make.py is part of an implicit namespace package. Add an __init__.py.
doc/scripts/eval_performance.py:1:1: INP001 File doc/scripts/eval_performance.py is part of an implicit namespace package. Add an __init__.py.
doc/source/conf.py:1:1: INP001 File doc/source/conf.py is part of an implicit namespace package. Add an __init__.py.
setup.py:1:1: INP001 File setup.py is part of an implicit namespace package. Add an __init__.py.
typings/numba.pyi:1:1: INP001 File typings/numba.pyi is part of an implicit namespace package. Add an __init__.py.
web/pandas_web.py:1:1: INP001 File web/pandas_web.py is part of an implicit namespace package. Add an __init__.py.

[twoertwein]

There are some new errors detected - will try to address or ignore them.

[twoertwein]

There are more errors with 1.1.291 microsoft/pyright#4546

[twoertwein]

The second commit fixes type issues uncovered by a newer pyright version. The third commit uses Sequence[Hashable] more consistently.

[mroeschke]

Looks good just a merge conflict

[twoertwein]

Looks good just a merge conflict

Rebased and green

[mroeschke]

Thanks @twoertwein