Clarify unsatisfied resource restrictions in resource docs

[peter941221]

Summary

• document that tasks with currently unsatisfied resource restrictions remain in the scheduler's no-worker state instead of failing immediately
• explain that this behavior follows from Dask clusters being dynamic and able to add matching workers later
• add practical guidance for users to avoid waiting indefinitely, including Future.result(timeout=...) and checking for no-worker

Closes #8256

Testing

• not run locally: sphinx is not installed in this environment

[github-actions]

Unit Test Results

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

    31 files  +    1      31 suites  +1   10h 37m 49s ⏱️ + 1m 24s
 4 080 tests ±    0   3 968 ✅ +    4    112 💤  -  1  0 ❌  - 2 
59 217 runs  +1 397  56 615 ✅ +1 334  2 602 💤 +66  0 ❌  - 2 

Results for commit 36f76cc. ± Comparison against base commit c9ef602.

♻️ This comment has been updated with latest results.

[peter941221]

Rebased on current main and pushed 8773991. CI is running again.

[crusaderky]

thank you!