fix: keep idle validation on native timers

[mcollina]

Summary

• use native timers for idle socket validation so fake timers do not block background cache revalidation

Tests

• node --test test/interceptors/cache.js
• node --test test/response-queue-poisoning.js test/issue-810.js
• npm run lint -- --quiet

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.25%. Comparing base (04ebc71) to head (4ebf1ca).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5397      +/-   ##
==========================================
- Coverage   93.26%   93.25%   -0.02%     
==========================================
  Files         110      110              
  Lines       36757    36826      +69     
==========================================
+ Hits        34283    34341      +58     
- Misses       2474     2485      +11     

☔ 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.