Fix #7354, Implementing NSE in cube

[sisyphuswastaken]

Pertains to issue #7354.
Changes implemented:

• isolated logic for processing SDcols from the [.data.table function, encapsulated it into a helper function .processSDcols.
• Added tests for code coverage
• removed the try-catch error block, to make errors more specific and debugging easier
  This PR continues work from Implementing NSE in cube #7540 and and Implementing NSE in cube #7543.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.03%. Comparing base (67e7840) to head (51d6916).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7603   +/-   ##
=======================================
  Coverage   99.02%   99.03%           
=======================================
  Files          87       87           
  Lines       16897    16939   +42     
=======================================
+ Hits        16733    16775   +42     
  Misses        164      164           

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[sisyphuswastaken]

I've added new tests for code coverage, and tried to undo the unnecessary changes that occurred when I had replaced the full function while integrating .processSDcols.

[sisyphuswastaken]

Hello! Bumping on this, let me know if any changes are to be made to the PR, I'd be happy to adjust :) @jangorecki

[jangorecki]

Tests should be made against pre-computed data. Otherwise we can mis a bug if it will be impacting both LHS and RHS of a tested code

[jangorecki]

I think the point to have helper function was to use it in [.data.table() too, or am I missing something?
And then I don't see it being used there.

The comment was in previous, now abandoned, PR: #7543 (comment)