[Python] Add __all__ variable in the package __init__.py file for Python APIs

[AAraKKe]

Hi team!

This PR is to address #17152. The way the package __init__.py file is done works at runtime but type checkers break because with the package being marked with py.typed all those imports are considered private.

The pyright type checker (behind the pylance language server for python in VSCode) has a good explanation about this in their docs. This makes that packages using API clients build with openapi-generator either need to have very verbose imports to import from the module the classes are defined in (turning the __init__.py import not usable) or have to disable the checker rules which can be undesired in some cases.

In order to fix it I have added the generation of the __all__ variable in the package __init__.py file that specifies the packages being exported explicitely. Type checkers now understand this and would not complaint about these imports.

The PR is against master because this has no impact in runtime so any API generate with this included or not will behave the same with the difference that type checks now would understand imports like

from myApi import ApiClient

Thanks!

CC: @cbornet, @tomplus, @krjakbrjak, @fa0311, @multani

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[wing328]

please follow step 3 to fix https://github.com/OpenAPITools/openapi-generator/actions/runs/14741549462/job/41394125780?pr=21185

[AAraKKe]

please follow step 3 to fix https://github.com/OpenAPITools/openapi-generator/actions/runs/14741549462/job/41394125780?pr=21185

Sorry I missed to add those after the latest update to remove the blank line! Should be fixed now.

Thanks for reviewing!

[AAraKKe]

@wing328 is there anything else needed to merge this? Let me know and I can take a look.

[wing328]

python 3.8 test failure can be ignored as these tests have been removed in the latest master

[wing328]

thanks for the PR

let's give it a try