v1.16.11-rc5

Use thread-per-request for async UDFs instead of shared event loop

The dedicated shared event loop still caused starvation under concurrent
async UDF calls. Switch to the same model used by sync UDFs: each request
gets its own thread with asyncio.run(), eliminating loop contention.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>