Polyfill: Speed up many-months date addition for calendars without leap months

[gibson042]

Ref #3153

This doesn't close the issue because it's limited to calendars with a fixed 12-month year, but I think it helps with those enough to justify.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.78%. Comparing base (ad9c6ff) to head (dea309e).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
polyfill/lib/calendar.mjs	0.00%	3 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3155      +/-   ##
==========================================
- Coverage   96.82%   96.78%   -0.04%     
==========================================
  Files          22       22              
  Lines       10084    10088       +4     
  Branches     1825     1826       +1     
==========================================
  Hits         9764     9764              
- Misses        270      273       +3     
- Partials       50       51       +1     

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[ptomato]

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