Data desegregation

[badasahog]

Data desegregation + minor formatting improvements + constness improvements

progress towards #6971

As an aside, I've been awaiting review for other PRs, #7248, #7247, #7244, #7238

[github-actions]

• HEAD=dataCodeIntegration3 slower P<0.001 for DT[by,verbose=TRUE] improved in #6296
• HEAD=dataCodeIntegration3 slower P<0.001 for isoweek improved in #7144
  

Generated via commit f0abdc4

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

Task	Duration
R setup and installing dependencies	4 minutes and 49 seconds
Installing different package versions	9 minutes and 50 seconds
Running and plotting the test cases	2 minutes and 39 seconds

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.09%. Comparing base (345e336) to head (f0abdc4).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7303   +/-   ##
=======================================
  Coverage   99.09%   99.09%           
=======================================
  Files          84       84           
  Lines       16096    16097    +1     
=======================================
+ Hits        15951    15952    +1     
  Misses        145      145           

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[rikivillalba]

Might conflict with 2db2a90 #7343