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 99.02%. Comparing base (9a8f664) to head (a8d3875).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #7603      +/-   ##
==========================================
- Coverage   99.04%   99.02%   -0.02%     
==========================================
  Files          87       87              
  Lines       17031    17095      +64     
==========================================
+ Hits        16868    16928      +60     
- Misses        163      167       +4     

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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

[sisyphuswastaken]

sorry for the delays, I was swamped with assignments but I'll push changes within this week. Also since I made a new branch, it seems as if some of my changes (the use of the helper function in [.data.table) weren't transferred properly. I'll fix that and have the changes ready for review within this week. I apologize for the inconvenience caused.

[sisyphuswastaken]

I've included the helper in [.data.table and added tests. Some might seem redundant since I added them for code coverage, which I'm still working on. I'm not yet sure how to tackle the project’s coverage checks failing, but I'm actively working on it.