fix tool_use id handling for anthropic models on session resume

[knQzx]

Summary

• when using anthropic models (claude) via ADK, resuming a session fails with BadRequestError because tool_use IDs get corrupted during replay
• two fixes: (1) preserve function call IDs for AnthropicLlm models in contents.py, (2) sanitize tool_use IDs in anthropic_llm.py so invalid/empty IDs get replaced with a valid generated ID instead of empty string

Test plan

• added 6 unit tests for _sanitize_tool_use_id (valid, None, empty, invalid chars)
• added 1 integration test for AnthropicLlm ID preservation in contents flow
• all 63 tests pass

fixes #5074

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[adk-bot]

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[knQzx]

I have signed the CLA