[Python SDK] Add unit tests for connection manager

[hed1ad]

Summary

Add comprehensive unit tests for the ConnectionManager module (sdk/python).

Coverage includes:

• Retry logic for transient failures
• Timeout handling
• Connection lifecycle (start, stop, reconnect)
• Health check monitoring
• Callbacks (on_connected, on_disconnected)
• Error handling for various failure scenarios

43 tests, all passing.

Testing

• ./scripts/test-all.sh
• Additional verification (please describe):

Checklist

• I updated documentation where applicable.
• I added or updated tests (or none were needed).
• I updated CHANGELOG.md (or this change does not warrant a changelog entry).

Screenshots (if UI-related)

N/A

Related issues

Close #122

[CLAassistant]

All committers have signed the CLA.

[santoshkumarradha]