Split unit test and unit race into 2 components

[GuptaManan100]

Description

This PR splits the unit_test and unit_race workflows into 2 parts, one that runs the evalengine tests only, and the other that runs everything else. This has been done because the CI workflows started taking too long and necessicated splitting them up.

The default behaviour of make unit_test and make unit_race doesn't change. In order to run restricted set of tests like we do in the CI, VTEVALENGINETEST environment variable has to be set to "1" or "-1".

Related Issue(s)

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
• If this change is to be back-ported to previous releases, a justification is included in the PR description
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on CI?
• Documentation was added or is not required

Deployment Notes

[vitess-bot]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.40%. Comparing base (178e6e8) to head (601ee33).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15734      +/-   ##
==========================================
+ Coverage   68.38%   68.40%   +0.01%     
==========================================
  Files        1556     1556              
  Lines      195361   195418      +57     
==========================================
+ Hits       133598   133666      +68     
+ Misses      61763    61752      -11     

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[deepthi]

Can you update the description to let people know how this affects make unit_test?