#22867 feat(python): enhance retry configuration in REST client

Description

Updated the retries parameter in the Python client Configuration so its type depends on the HTTP library:

• urllib3: Retry | int | None — passed through to the pool as connection pool kwargs (key_retries).
• asyncio: int | aiohttp_retry.RetryOptionsBase | None — int is turned into ExponentialRetry; otherwise the given RetryOptionsBase instance is used.

Type annotation: Optional[Union[int, Any]]. No isinstance checks in the urllib3 client as it does not require one; retries are passed through as-is.

Implements #17011

Other python generators, like httpx, tornado, etc. are out of scope as they either have no native retry mechanism or no maintained third party libraries

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Checklist (unchanged from your template):

• Read the contribution guidelines
• Pull Request title clearly describes the work and description provides detail
• Run the following to build the project:

  ./mvnw clean package || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  Commit all changed files. CI verifies all generator outputs.
• File the PR against the correct branch
• If your PR solves a reported issue, reference it using GitHub's linking syntax
• If your PR targets a particular programming language, @mention the technical committee

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Summary by cubic

Make the Python client's retry config transport-aware. Configuration.retries now accepts int or library-specific options for urllib3 and asyncio, enabling custom retry strategies and addressing #17011.

• New Features
  • urllib3: accepts int or urllib3 Retry; value passed through unchanged.
  • asyncio: accepts int or aiohttp_retry.RetryOptionsBase; int converts to ExponentialRetry and is reused.
  • Updated type hints/docs to Optional[Union[int, Any]] and clarified behavior in Configuration.