test: stabilize HTTP/2 timeout tests

[mcollina]

Skip the HTTP/2 churn stress test on Linux Node.js 24 and 25, where nodejs/node#64841 can terminate the process before the test reports an assertion. Keep the test enabled on unaffected platforms and Node.js versions, and release each seed's resources before the next seed runs.

Make the issue #5087 timeout tests own and await their HTTP/2 teardown, cancel delayed server work, and only tolerate the reset errors expected from intentionally timed-out streams. This supersedes #5643 with the additional Node.js 25 and timeout-test fixes.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.46%. Comparing base (692c02b) to head (5a7fc99).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5689      +/-   ##
==========================================
- Coverage   93.46%   93.46%   -0.01%     
==========================================
  Files         110      110              
  Lines       38777    38777              
==========================================
- Hits        36244    36243       -1     
- Misses       2533     2534       +1     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.