Cache occupancy in WorkStealing.balance()

[hendrikmakait]

Calculating the occupancy is somewhat expensive, so we should avoid it if possible.

• Tests added / passed
• Passes pre-commit run --all-files

[github-actions]

Unit Test Results

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

    27 files  +  1      27 suites  +1   11h 31m 44s ⏱️ + 40m 42s
 4 118 tests +  7   4 004 ✅ + 11    111 💤  -  2  3 ❌  - 1 
51 641 runs  +419  49 340 ✅ +363  2 297 💤 +57  4 ❌ ±0 

For more details on these failures, see this check.

Results for commit 6917e8b. ± Comparison against base commit b86b714.

This pull request removes 2 and adds 9 tests. Note that renamed tests count towards both.

distributed.cli.tests.test_dask_worker.test_listen_address_ipv6[tcp:..[ ‑ 1]:---nanny]
distributed.cli.tests.test_dask_worker.test_listen_address_ipv6[tcp:..[ ‑ 1]:---no-nanny]

distributed.diagnostics.tests.test_memray ‑ test_basic_integration_scheduler
distributed.diagnostics.tests.test_memray ‑ test_basic_integration_scheduler_report_args[False]
distributed.diagnostics.tests.test_memray ‑ test_basic_integration_scheduler_report_args[report_args0]
distributed.diagnostics.tests.test_memray ‑ test_basic_integration_workers[1]
distributed.diagnostics.tests.test_memray ‑ test_basic_integration_workers[False]
distributed.diagnostics.tests.test_memray ‑ test_basic_integration_workers[True]
distributed.diagnostics.tests.test_memray ‑ test_basic_integration_workers_report_args[False]
distributed.diagnostics.tests.test_memray ‑ test_basic_integration_workers_report_args[report_args0]
distributed.tests.test_steal ‑ test_stealing_objective_accounts_for_in_flight