fix(sdk): support async generator functions in control() decorator

[KazChe]

Summary

• adds async generator (streaming) support to the control() decorator, fixing crashes and silent bypasses when applied to async def functions with yield — the standard pattern for LLM response streaming.

Scope

• User-facing/API changes: @control() now correctly wraps async generator functions, preserving inspect.isasyncgenfunction() identity
• Internal changes: New async_gen_wrapper path in control() that runs pre-check before first chunk, yields chunks in real-time while accumulating, and runs post-check on full accumulated output after stream completes
• Out of scope: Sync generator support, per-chunk evaluation

Risk and Rollout

• Risk level: low
• Rollback plan: Revert commit — the change is additive (new code path) with no modifications to existing sync/async wrapper logic

Testing

• Added or updated automated tests
• Ran make check (lint + typecheck pass; server tests have pre-existing postgres failures unrelated to this change)
• Manually verified behavior

Checklist

• Linked issue/spec (if applicable) — Closes control() decorator can break on streaming (async generator) functions for agents that have stream=true for latency. #113
• Updated docs/examples for user-facing changes
• Included any required follow-up tasks

[KazChe]

Hihi, sdk-ts-ci check failin due to a missing SPEAKEASY_API_KEY secret that'snot available to fork PRs and unrelated to the changes in this PR (python sdk only)