fix(js/ts/python): settle cancelled delays and finalizers once

[dbrattli]

Why

Python Async.Sleep discards its scheduled handle, so cancellation can later be followed by timeout success and a second finalizer. The cancellation guard also falls through and executes already-cancelled work. JS leaves cancelled-sleep listeners installed, and both runtimes mishandle throwing finalizers during cancellation. Executed .NET references confirm that cancellation stays terminal even if its finalizer throws.

The regressions belong in the existing F# async suites so they exercise generated computations and share public behavior checks with .NET. Native fixtures provide deterministic scheduler and thread controls through the suites' established interop pattern.

How

• Retain the Python timer handle and arbitrate timeout/cancellation once, retiring the timer and listener on success, cancellation, and scheduler installation failure.
• Marshal foreign-thread cancellation to the owning live event loop and dispose registrations outside the settlement gate.
• Stop Python work after the initial cancellation continuation and make finalizers run once; ordinary finalizer failures use the error continuation, while cancellation-time failures preserve cancellation as on .NET.
• Give JS sleep the same single-settlement cleanup and finalizer behavior.
• Put test cases, assertions, and async computations in tests/Python/TestAsync.fs and tests/Js/Main/AsyncTests.fs. Import scheduler/thread fixtures from tests/Python/py/async_runtime.py and tests/Js/Main/js/async-runtime.js; remove the standalone JS runner and its build hook.
• Preserve stale-callback execution after timer retirement, installation barriers/failures, cleanup counters, real-thread owner-loop checks, and caller-owned reply/cancel/timeout arbitration for every controlled winner. Run shared finalizer failure checks against .NET as well as generated targets.
• Document and regress existing idle mailbox limits: token cancellation alone does not wake Receive. Python observes it on a post; JS later delivers the posted message.

[github-actions]

Python Type Checking Results (Pyright)

Metric	Value
Total errors	34
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	12	Excluded
temp/tests/Python/test_nested_and_recursive_pattern.py	2	Excluded
temp/tests/Python/fable_modules/thoth_json_python/encode.py	2	Excluded