[unsupervised AI] fix: propagate task annotations during worker execution

[rohitsalla]

Fixes #9138

What changed

• Enter resolved user annotation context while worker user code executes, instead of propagating only the span annotation.
• Keep scheduler and execution controls such as worker restrictions, resources, retries, and executor selection scoped to the parent task.
• Add regression coverage for nested synchronous and asynchronous delayed computations, sequential spans, and control-annotation isolation.

This lets nested distributed computations inherit user annotations without accidentally constraining child scheduling to the parent task.

Verification

• .venv/bin/python -m pytest -q distributed/tests/test_worker_client.py distributed/tests/test_spans.py
  • 51 passed, 1 skipped (optional pandas dependency), 1 xpassed
• .venv/bin/python -m pytest -q distributed/tests/test_actor.py::test_serialize_with_pickle
  • 1 passed
• .venv/bin/python -m pytest -q -o addopts='' -W default::pytest.PytestUnknownMarkWarning distributed/tests/test_client.py::test_secede_balances distributed/tests/test_worker.py::test_get_client
  • 2 passed; local environment lacks the optional flaky-marker plugin
• .venv/bin/python -m ruff check distributed/worker.py distributed/tests/test_worker_client.py
• .venv/bin/python -m ruff format --check distributed/worker.py distributed/tests/test_worker_client.py
• git diff --check

[github-actions]

Unit Test Results

See test report for an extended history of previous test failures. This is useful for diagnosing flaky tests.

    40 files  ± 0      40 suites  ±0   14h 45m 0s ⏱️ - 10m 9s
 4 160 tests + 1   3 979 ✅  -  1    178 💤 ±0  3 ❌ +2 
80 960 runs  +21  76 719 ✅ +17  4 238 💤 +2  3 ❌ +2 

For more details on these failures, see this check.

Results for commit 696800c. ± Comparison against base commit 40fcd99.

♻️ This comment has been updated with latest results.