Allow setnafill() to accept logical vectors in cols (#4113)

[venom1204]

CLOSES #4113

this PR enables setnafill() to accept logical vectors for the cols argument, allowing for dynamic column selection via conditions like sapply(DT, is.numeric). The implementation updates the internal colnamesInt C utility to handle logical vectors with exact length matching and NA validation while ensuring that existing error-handling logic remains consistent across the package.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.01%. Comparing base (accac97) to head (986c878).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7842      +/-   ##
==========================================
- Coverage   99.01%   99.01%   -0.01%     
==========================================
  Files          88       88              
  Lines       17288    17293       +5     
==========================================
+ Hits        17118    17122       +4     
- Misses        170      171       +1     

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[github-actions]

• HEAD=issue41113 much slower for transform improved in #5493
• HEAD=issue41113 much slower for fread disk overhead improved in #6925
• HEAD=issue41113 faster P<0.001 for memrecycle regression fixed in #5463
• HEAD=issue41113 faster P<0.001 for DT[by,verbose=TRUE] improved in #6296
  

Generated via commit 986c878

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

Task	Duration
R setup and installing dependencies	2 minutes and 51 seconds
Installing different package versions	1 minutes and 10 seconds
Running and plotting the test cases	5 minutes and 35 seconds

[ben-schwen]

Calling colnamesInt here seems the wrong approach to me, since we also call it in nafillR. Something simple as without additional C logic

if (is.logical(cols)) {
  if (length(cols) != length(x)) stopf("'cols' is a logical vector of length %d but there are %d columns", length(cols), length(x))
  if (anyNA(cols)) stopf("'cols' contains NA at position %d", which(is.na(cols))[1L])
  cols = which(cols)
}

[ben-schwen]

please rather use a setup step, then trying to do everything in one step.
Also, most of the time we test against fixed values. If you really want to test integer indices versus logical indexing, I would suggest

Suggested change

	test(2382.01, {DT = data.table(a=c(1,NA,3), b=c(4,NA,6), c=c(7,NA,9)); DT1 = copy(DT); DT2 = copy(DT); setnafill(DT1, type="locf", cols=c(TRUE,FALSE,TRUE)); setnafill(DT2, type="locf", cols=c(1L,3L)); identical(DT1, DT2)}, TRUE)
	DT = data.table(a=c(1,NA,3), b=c(4,NA,6), c=c(7,NA,9))
	test(2382.01, setnafill(copy(DT), type="locf", cols=c(TRUE,FALSE,TRUE)), setnafill(copy(DT), type="locf", cols=c(1L,3L)))

[ben-schwen]

why do we need this line?