Simplify Scheduler.restart logic

[hendrikmakait]

Closes #xxxx

• 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.

       15 files  ±  0         15 suites  ±0   6h 6m 30s ⏱️ - 27m 57s
  3 154 tests  -   2    3 061 ✔️  -   3    83 💤  -   3  10 ❌ +  4 
23 332 runs   - 17  22 392 ✔️  - 20  899 💤  - 17  41 ❌ +20 

For more details on these failures, see this check.

Results for commit 25dc163. ± Comparison against base commit 0983731.

♻️ This comment has been updated with latest results.

[jrbourbeau]

@hendrikmakait I've not looked too closely at the changes here but they seem (at least indirectly) related to #7154. I was planning to push on some of your suggestions in #7154 -- should I hold off and wait for this PR to land first?

[hendrikmakait]

@jrbourbeau: If you want to get the feature out, I think it's fine to merge #7154 without waiting for this. I can take care of adjustments that utilize the changes made here to improve alignment between Client.restart and Client.restart_workers. For context, this PR is sparked by a discussion with @fjetter around #7154 and the way Client.restart is currently implemented.

[hendrikmakait]

Superseded by #7242