[python] Add client versions to REST User-Agent.

[zhoulii]

Purpose

close #8543

Tests

[JingsongLi]

Directly changing the public configuration key 'header. HTTP_SUSER_AGENT' to 'header. User Agent' is not compatible with the old key. Reproduced locally: The old configuration will be silently ignored, and the actual sending will default to 'PyPaimon/...'; Depreciated/fallback compatibility should be retained.

[zhoulii]

Directly changing the public configuration key 'header. HTTP_SUSER_AGENT' to 'header. User Agent' is not compatible with the old key. Reproduced locally: The old configuration will be silently ignored, and the actual sending will default to 'PyPaimon/...'; Depreciated/fallback compatibility should be retained.

Thanks for pointing this out. I added Java-aligned fallback-key support on the Python side: header.User-Agent remains the canonical key, while the legacy header.HTTP_USER_AGENT is retained as a fallback. The legacy value is now correctly sent as the User-Agent header instead of falling back to
PyPaimon/....

[JingsongLi]

cc @sundapeng to take a look.