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  ±0      31 suites  ±0   10h 57m 2s ⏱️ + 17m 11s
 4 074 tests ±0   3 967 ✅  - 2    104 💤 ±0  2 ❌ +1  1 🔥 +1 
59 132 runs  +1  56 696 ✅  - 2  2 433 💤 +1  2 ❌ +1  1 🔥 +1 

For more details on these failures and errors, see this check.

Results for commit 945d7eb. ± Comparison against base commit d8fabe2.