switch to snake case

[badasahog]

In many other places in the code, if is spelled iff. I didn't fix the others to avoid creating conflicts.

Also, I've updated type case to snake case. The codebase is mostly snake case, so that's what I think we should go with. If you agree, I will do so more comprehensively.

[aitap]

In many other places in the code, `if` is spelled `iff`.

That's an abbreviation for <https://en.wikipedia.org/wiki/If_and_only_if>.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.10%. Comparing base (59692e7) to head (017cecd).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7325   +/-   ##
=======================================
  Coverage   99.10%   99.10%           
=======================================
  Files          84       84           
  Lines       16128    16128           
=======================================
  Hits        15983    15983           
  Misses        145      145           

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[github-actions]

• HEAD=fixSpelling slower P<0.001 for isoweek improved in #7144
  

Generated via commit d38996b

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

Task	Duration
R setup and installing dependencies	2 minutes and 52 seconds
Installing different package versions	43 seconds
Running and plotting the test cases	2 minutes and 43 seconds

[badasahog]

@aitap understood. reverting.