[dbrattli]

Summary

Python's Async replacement accepted several F# members without corresponding runtime functions. This adds Async.Choice, Async.OnCancel, and Async.StartImmediateAsTask, plus cancellable Task.Delay and direct Async<'T> binding and return! in task { }.

Compiled Async.StartChild now uses a new start_child_linked runtime entry point: it starts its child when the outer async runs, links the child's token to the parent, and cancels the underlying child when a timeout expires. The existing Python start_child function keeps its published behavior. A timeout still leaves the parent token usable, and a child-raised timeout exception keeps its original identity.

Async.Choice converts Fable enumerables through the runtime iterator adapter, which also keeps its generated Python type correct. The Python async and task suites exercise the new members and timeout behavior through F# on .NET and generated Python.

Python counterpart to #5097.

[github-actions]

Python Type Checking Results (Pyright)

Metric	Value
Total errors	33
Files with errors	4
Excluded files	4
New errors	✅ No

Excluded files with errors (4 files)

These files have known type errors and are excluded from CI. Remove from pyrightconfig.ci.json as errors are fixed.

File	Errors	Status
temp/tests/Python/test_hash_set.py	18	Excluded
temp/tests/Python/test_applicative.py	11	Excluded
temp/tests/Python/test_nested_and_recursive_pattern.py	2	Excluded
temp/tests/Python/fable_modules/thoth_json_python/encode.py	2	Excluded