python: simplify lazy-import type-checking guards

[tamird]

The lazy Python initializers use dynamic __import__ to reach typing.TYPE_CHECKING, an idiom introduced alongside lazy-imports in c4a7c14.

Use a private standard-library typing module import instead. This keeps type-checking branches statically recognizable, avoids shadowing generated models named TYPE_CHECKING, and leaves clients without lazy imports unchanged.

[tamird]

@wing328 could you please TAL?

[cubic-dev-ai]

No issues found across 6 files

_{Re-trigger cubic}

[wing328]

thanks for the PR. will review and try to get it merged

cc @cbornet (2017/09) @tomplus (2018/10) @krjakbrjak (2023/02) @fa0311 (2023/10)

[fa0311]

This is clearer and easier to read than using __import__(). I don’t see any behavioral issues. LGTM.

[tamird]

Thanks @wing328! FYI this is going to have a minor merge conflict with #24402 which is a much more important but also more complex change. I would be very thankful if you could prioritize landing both. They are currently required to unblock updating kubernetes-client to the latest openapi-generator release, which is a very big milestone! See discussion in kubernetes-client/python#2631.

Thanks for your help so far! I'm very excited to ship this long-overdue update for kubernetes-python.