fix(cli): handle sync/async serve functions in m serve

[markstur]

Misc PR

Type of PR

• Bug Fix
• New Feature
• Documentation
• Other

Description

• Link to Issue: Part of: Create OpenAI API-compatible HTTP interface for mellea #521

fix(cli): handle sync/async serve functions in m serve

Fixes sync/async mismatch in `m serve` by detecting function type and
handling appropriately:
- Async serve functions are awaited directly
- Sync serve functions are wrapped in asyncio.to_thread() to prevent
  blocking FastAPI's event loop

This ensures the server can handle concurrent requests efficiently
regardless of whether user-defined serve functions are sync or async.

Changes:
- cli/serve/app.py: Add asyncio/inspect imports, update make_chat_endpoint()
  to detect coroutine functions and wrap sync functions in to_thread()
- test/cli/test_serve_sync_async.py: Add comprehensive test suite (9 tests)
  including empirical timing test that proves non-blocking behavior

feat: Map OpenAI parameters to ModelOption sentinels:

   - temperature → ModelOption.TEMPERATURE
   - max_tokens → ModelOption.MAX_NEW_TOKENS
   - seed → ModelOption.SEED


Signed-off-by: Mark Sturdevant <mark.sturdevant@ibm.com>

Testing

• Tests added to the respective file if code was changed
• New code has 100% coverage if code as added
• Ensure existing tests and github automation passes (a maintainer will kick off the github automation when the rest of the PR is populated)

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