WIP: openai function call interface (DO NOT MERGE!!!)

[tsubasakong]

Pull Request Title

WIP: openai function call interface (DO NOT MERGE!!!)

Description

This older draft PR covers OpenAI function/tool-calling compatibility updates. The original WIP title is preserved above because the PR is still marked DO NOT MERGE.

Related Issues / Tickets

None linked in the current PR description.

How Has This Been Tested?

No fresh verification was recorded in the original PR description, and no additional local test run was performed in this maintenance pass.

Checklist

• Documentation: I have updated or added documentation where needed (in code, README, or other docs).
• Tests:
  • Added or updated tests to cover my changes. All tests pass locally on my machine.
  • I have added a test script in mesh/tests/ that instantiates my mesh agent and calls its handle_message with example input.
  • No tests needed for this PR.
• Metadata (for Heurist Mesh Agents): I have filled out or updated the agent’s metadata (name, description, author, inputs/outputs, etc.) if relevant.
• No Duplicates: I have checked that no other PR is addressing the same issue or feature.
• No Breaking Changes: The changes in this PR do not break existing functionality. If they do, I have clearly explained the impact below.

Additional Notes

Original draft notes were minimal, so no extra context was available to preserve here.