Add/fix unit tests for direct_compress_insert

[natalya-aksman]

Fix a typo in the unit test (meant to be reverse order but non-reverse order was actually used) plus added more test cases.

Disable-check: approval-count

Can wait until the next release as no new issues with direct compress insert were uncovered.

[github-actions]

@erimatnor, @akuzm: please review this pull request.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.54%. Comparing base (904c928) to head (f9592c0).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8843      +/-   ##
==========================================
+ Coverage   82.46%   82.54%   +0.07%     
==========================================
  Files         248      248              
  Lines       47946    47920      -26     
  Branches    12224    12220       -4     
==========================================
+ Hits        39539    39555      +16     
- Misses       3503     3516      +13     
+ Partials     4904     4849      -55     

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