Add spans to Fine Performance Metrics bokeh dashboard

[crusaderky]

• Part of Fine performance metrics meta-issue #7665
• Part of User-defined spans #7860

[github-actions]

Unit Test Results

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

       20 files  ±    0         20 suites  ±0   12h 29m 57s ⏱️ + 1h 2m 9s
  3 679 tests ±    0    3 571 ✔️ +    5     106 💤  -   2  2 ❌  - 3 
35 763 runs  +183  34 082 ✔️ +271  1 679 💤  - 85  2 ❌  - 3 

For more details on these failures, see this check.

Results for commit 22613f6. ± Comparison against base commit 74a1bcd.

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

distributed.protocol.tests.test_numpy
distributed.shuffle.tests.test_rechunk

distributed.tests.test_spans ‑ test_merge_by_tags
distributed.tests.test_spans ‑ test_merge_by_tags_metrics