Run each async udf in its own thread

[nkitsaini]

Note

Medium Risk
Changes core UDF dispatch and asyncio/thread lifecycle (including background tasks outliving requests); publish workflow behavior affects release versioning and when PyPI uploads run.

Overview
Async external UDFs no longer run on the ASGI event loop or spin up a fresh loop per call via asyncio.run(). Every invoke now runs in a thread pool worker with a persistent per-thread event loop, so loop-bound clients (e.g. httpx pools) can be reused and teardown “event loop is closed” errors are avoided.

Cancellation is wired through _cancellable_run (polls cancel_event) and the handler sets cancel_event when the worker task is still pending on timeout/disconnect, plus in finally, so cancellation reaches code inside the worker loop—not only the outer asyncio task.

Publish workflow: on pre-release tag pushes, pyproject.toml is rewritten to PEP 440 versions (-testN → .devN, -alpha/-beta/-rc → a/b/rc). PyPI publish runs on release or workflow_dispatch with publish_pypi, not on tag push alone.

Adds test_udf_event_loop.py covering loop reuse, cancellation timing, exceptions, context vars, and concurrency.

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Release rebuild skips version patch

Medium Severity

The new pre-release pyproject.toml rewrite runs only when github.event_name == 'push', but the same workflow also runs on release: published and publishes to PyPI from that run’s freshly built artifacts. A published GitHub Release for a pre-release tag can therefore ship wheels/sdists whose metadata was never converted to a valid PEP 440 version.

 

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[kesmit13]

This isn't an issue. The remapping of wheel names should only happen with pre-release pushes, not the actual releases.