TYP: Fix typehints for ExtensionDtype

[ozars]

This is a fix for type hints of ExtensionDtype. register_extension_dtype was confusing pyright autocomplete. It was fixed by parameterizing its return value on its input value.

Example:

import pandas as pd

pd.CategoricalDtype(categories=['a', 'b'])

Before this change:

$ pyright --version
pyright 1.1.133
$ pyright --lib pd.py
No configuration file found.
No pyproject.toml file found.
stubPath /home/omer/src/ext/typings is not a valid directory.
Assuming Python platform Linux
Searching for source files
Found 1 source file
/home/omer/src/ext/pd.py
  /home/omer/src/ext/pd.py:3:1 - error: Expected no arguments to "ExtensionDtype" constructor (reportGeneralTypeIssues)
1 error, 0 warnings, 0 infos
Completed in 0.72sec

After:

$ pyright --lib ../pd.py
No configuration file found.
pyproject.toml file found at /home/omer/src/ext/pandas.
Loading pyproject.toml file at /home/omer/src/ext/pandas/pyproject.toml
Pyproject file "/home/omer/src/ext/pandas/pyproject.toml" is missing "[tool.pyright] section.
stubPath /home/omer/src/ext/pandas/typings is not a valid directory.
Assuming Python platform Linux
Searching for source files
Found 1 source file
0 errors, 0 warnings, 0 infos
Completed in 0.777sec

[ozars]

pyright was yelling at me that return dtype_type.construct_from_string(dtype) actually returns ExtensionDtype from find. I tried fixing it while I was at it but reverted back later since it broke things elsewhere with mypy. This part should be irrelevant to the rest.

pandas/pandas/core/dtypes/base.py

Line 427 in ac2e3e6

def find(self, dtype: type[ExtensionDtype] | str) -> type[ExtensionDtype] | None:

This should be ready for review if it passes CI. This is a very minor change but it helps removing # type: ignore in some cases with extension dtypes in the user code, keeping type checker and autocompleter happy.

[jreback]

cc @simonjayhawkins @Dr-Irv

[simonjayhawkins]

lgtm @Dr-Irv register_extension_dtype was not giving pyright warnings in #39501?

[Dr-Irv]

lgtm @Dr-Irv register_extension_dtype was not giving pyright warnings in #39501?

@simonjayhawkins
I may have been using an earlier version of pyright. But I think it would be better to merge in #40421 and then see if this PR is needed, because #40421 handles many ExtensionDType things.

[simonjayhawkins]

#40421 has conflicts and needs a merge master anyway. let's get this one in.

[simonjayhawkins]

Thanks @ozars small targeted PRs for adding/refining type annotations always welcome.

[ozars]

Thank you.