feat(calendar): add cell slot

[jahnli]

close #6017

[vercel]

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[codecov-commenter]

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Codecov Report

❌ Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 58.30%. Comparing base (91187f1) to head (4543ba4).

Files with missing lines	Patch %	Lines
src/calendar/src/Calendar.tsx	66.66%	0 Missing and 1 partial ⚠️
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Additional details and impacted files

@@           Coverage Diff           @@
##             main    #7258   +/-   ##
=======================================
  Coverage   58.30%   58.30%           
=======================================
  Files        1178     1178           
  Lines       26109    26110    +1     
  Branches     6543     6543           
=======================================
+ Hits        15222    15223    +1     
+ Misses       8374     8373    -1     
- Partials     2513     2514    +1     

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