test: reduce retry-after invalid date timing flake

[trivikr]

This relates to...

• Fixes: [flaky] test/retry-handler2.js #5217
• Similar to test: reduce retry-after invalid date flake #4788

Rationale

The throwOnError: false retry-handler test had the same intermittent timing issue that was previously fixed in test/retry-handler.js. The assertion used wall-clock time with an exact lower bound, which can be flaky around timer scheduling boundaries.

Changes

• Reduce flakiness in the invalid retry-after date test in test/retry-handler2.js
• Use monotonic time via process.hrtime.bigint()
• Allow a small scheduling tolerance around the configured minTimeout

Features

N/A

Bug Fixes

N/A

Breaking Changes and Deprecations

N/A

Status

• I have read and agreed to the Developer's Certificate of Origin
• Tested
• Benchmarked (optional)
• Documented
• Review ready
• In review
• Merge ready

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.27%. Comparing base (2b0d4c9) to head (28ee419).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5250   +/-   ##
=======================================
  Coverage   93.27%   93.27%           
=======================================
  Files         110      110           
  Lines       36366    36366           
=======================================
  Hits        33922    33922           
  Misses       2444     2444           

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