test: fix flaky test-performance-eventloopdelay

[mcollina]

Summary

• Fixes flaky test test/sequential/test-performance-eventloopdelay.js
• The test was failing intermittently on IBM sharedlibs containers

Problem

The test was flaky because the histogram sampling might not have completed
before the assertions ran. The assertion assert(histogram.min > 0) could
fail if no samples were recorded yet.

Solution

• Wrapped the assertions in setImmediate(common.mustCall(() => {...})) to
  give the event loop a chance to record final samples before checking
• Added an explicit check for histogram.count > 0 to provide a clearer
  error message if no samples are recorded

Verification

Verified with python3 tools/test.py --repeat 50 without failures.

Refs: nodejs/reliability#1450

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.67%. Comparing base (27a7bbc) to head (25ea05c).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #61629      +/-   ##
==========================================
- Coverage   89.76%   89.67%   -0.09%     
==========================================
  Files         673      673              
  Lines      203945   203926      -19     
  Branches    39191    39136      -55     
==========================================
- Hits       183076   182877     -199     
- Misses      13198    13345     +147     
- Partials     7671     7704      +33     

see 40 files with indirect coverage changes

🚀 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.