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]

Response from ADK Triaging Agent

Hello @knQzx, thank you for your contribution!

Before we can merge this PR, you'll need to sign the Contributor License Agreement (CLA). You can do so by following the instructions at https://cla.developers.google.com/.

Thanks!

[knQzx]

I have signed the CLA

[rohityan]

Hi @knQzx , Thank you for your contribution through this pull request! This PR has merge conflicts that require changes from your end. Could you please rebase your branch with the latest main branch to address these? Once this is complete, please let us know so we can proceed with the review.

[rohityan]

Hi @wukath , can you please review this.

[knQzx]

@rohityan merged main, ready for review