fix: fix error in metrics.ts related to this.#cacheMissWindows.delete(firstKey)

[schaeferka]

Description

this.#cacheMissWindows.delete(firstKey) is generating an error related to it possibly being undefined. This should be investigated and fixed.

...

End to End Test:
(See Pepr Excellent Examples)

Related Issue

Fixes #1351

Relates to #

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Other (security config, docs update, etc)

Checklist before merging

• Unit, Journey, E2E Tests, docs, adr added or updated as needed
• Contributor Guide Steps followed

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.02%. Comparing base (224bdd8) to head (253dce5).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1352      +/-   ##
==========================================
+ Coverage   78.01%   78.02%   +0.01%     
==========================================
  Files          35       35              
  Lines        1669     1670       +1     
  Branches      370      396      +26     
==========================================
+ Hits         1302     1303       +1     
+ Misses        365      338      -27     
- Partials        2       29      +27     

Files with missing lines	Coverage Δ
src/lib/metrics.ts	100.00% <100.00%> (ø)

... and 7 files with indirect coverage changes