Polyfill: Speed up Chinese calendar getMonthList

[gibson042]

Noticed in passing.

[codecov]

Codecov Report

❌ Patch coverage is 98.57143% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 96.80%. Comparing base (1a089eb) to head (abe0d54).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
polyfill/lib/calendar.mjs	98.14%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3156      +/-   ##
==========================================
- Coverage   96.80%   96.80%   -0.01%     
==========================================
  Files          22       22              
  Lines       10131    10129       -2     
  Branches     1834     1835       +1     
==========================================
- Hits         9807     9805       -2     
  Misses        273      273              
  Partials       51       51              

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[ptomato]

I didn't have time to get a full understanding of this change, but it looks correct. I do get about a 1% speedup measuring differences over various year ranges.

If you like I can write a snapshot test comparing some results before and after.

[gibson042]

If you like I can write a snapshot test comparing some results before and after.

Thanks; that'd be great!

[ptomato]

Yep, preserves all the results, including existing bugs, when run against 65884 pairs of various dates between 1900 and 2100 (the non-implementation-approximated validity range for this calendar)