Infer cols from named order in setorderv() (#6932)

[venom1204]

closes #6932

This PR resolves the issue allowing setorderv() to infer column names from a named order vector when the cols argument is omitted. This change reduces redundancy by eliminating the need to provide column names twice. The implementation includes a new safety check to error on duplicate names in the order mapping, and both man/setorder.Rd and NEWS.md have been updated to document the new functionality.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.01%. Comparing base (accac97) to head (ce0f42b).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7861   +/-   ##
=======================================
  Coverage   99.01%   99.01%           
=======================================
  Files          88       88           
  Lines       17288    17291    +3     
=======================================
+ Hits        17118    17121    +3     
  Misses        170      170           

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[github-actions]

• HEAD=issue6932 much slower for transform improved in #5493
• HEAD=issue6932 slower P<0.001 for DT[by,verbose=TRUE] improved in #6296
  

Generated via commit b9c4405

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

Task	Duration
R setup and installing dependencies	6 minutes and 32 seconds
Installing different package versions	12 minutes and 57 seconds
Running and plotting the test cases	5 minutes and 35 seconds