test: avoid timer race in event loop delay test

[trivikr]

Refs: https://github.com/nodejs/reliability/issues?q=sort%3Aupdated-desc%20test-performance-eventloopdelay

Problem

The test enables the histogram and checks it from a 20 ms timer.

On slow or contended systems, that timer can expire before the first complete event loop iteration.
The timer then disables the histogram before its uv_check callback records a sample.

Previous fixes addressed related but distinct failures:

• test: fix flaky test-performance-eventloopdelay #61629 deferred assertions for the interval-based histogram.
• test: relax min assertion in test-performance-eventloopdelay #63100 allowed a valid minimum histogram value of zero.

The failing samplePerIteration checks were added later by #62935 and still depend on elapsed time.

Solution

Drive a known number of event loop iterations using setImmediate before disabling and checking each histogram.

The default-resolution and large-resolution checks share one iteration chain, removing the duplicated timing logic.

---

Assisted-by: codex:gpt-5.6-sol

[trivikr]

Stress tests on

• main: https://ci.nodejs.org/job/node-stress-single-test/806/
• PR: https://ci.nodejs.org/job/node-stress-single-test/810/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.32%. Comparing base (bfa3e98) to head (f862517).
⚠️ Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #64728      +/-   ##
==========================================
- Coverage   90.32%   90.32%   -0.01%     
==========================================
  Files         760      760              
  Lines      249130   249130              
  Branches    47041    47041              
==========================================
- Hits       225030   225023       -7     
- Misses      15490    15494       +4     
- Partials     8610     8613       +3     

see 24 files with indirect coverage changes

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