Add limit parameter to nafill and setnafill #7677

[venom1204]

closes #7677

this PR adds a limit argument to nafill and setnafill to restrict the maximum number of consecutive NA values filled. Default is Inf to preserve existing behavior. Updated R interface, C kernel logic, and documentation.

hi @tdhock @joshhwuu can you please have a look at this when you got time thanks .

[codecov]

Codecov Report

❌ Patch coverage is 83.82353% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 98.95%. Comparing base (94649d5) to head (dd875ac).

Files with missing lines	Patch %	Lines
src/nafill.c	85.48%	9 Missing ⚠️
R/shift.R	66.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7819      +/-   ##
==========================================
- Coverage   99.01%   98.95%   -0.07%     
==========================================
  Files          88       88              
  Lines       17234    17285      +51     
==========================================
+ Hits        17065    17105      +40     
- Misses        169      180      +11     

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[github-actions]

• HEAD=issue777666777 much slower for transform improved in #5493
  

Generated via commit dd875ac

Download link for the artifact containing the test results: ↓ atime-results.zip

Task	Duration
R setup and installing dependencies	6 minutes and 28 seconds
Installing different package versions	11 minutes and 34 seconds
Running and plotting the test cases	5 minutes and 21 seconds