[Tech Debt] Add unit tests for tool schema conversion utilities (api/tools/utils.py) #814

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Description

The four schema-conversion helpers in python/flink_agents/api/tools/utils.py
have no direct unit tests:

• create_schema_from_function
• create_model_from_schema
• create_model_from_java_tool_schema_str
• create_java_tool_schema_str_from_model

They are used by the Java/Python cross-language tool bridge, but are only
exercised incidentally today, so their conversion logic is effectively
untested.

Proposed fix

add a tests/ package under api/tools/ with focused unit
tests for each function (including a round-trip test for the inverse pair).
Test-only change, no production code touched.

Are you willing to submit a PR?

• I'm willing to submit a PR!