[FEATURE]: Python's agent library should add the version number when creating an A2UI data part

In [this code](https://github.com/a2ui-project/a2ui/blob/453bfa07b624b5b9877c47c22e235170f3e82f6f/agent_sdks/python/a2ui_agent/src/a2ui/a2a/parts.py#L34) the version number presence in the data is not checked. If it's missing - this library should add the version because it's required in 0.9 and above.

The issue points to the specific file agent_sdks/python/a2ui_agent/src/a2ui/a2a/parts.py line 34. Start by examining the function that creates the data part and understand the version requirement for A2UI 0.9+. Check if the version field is present; if missing, add it. Run existing tests for the Python agent library to ensure the change doesn't break anything. Verify the change by creating a test data part and confirming the version is included.

Written by the indexing model from the issue text.