test: refine coverage report

[Belco90]

Checks

• I have read the contributing guidelines.

Changes

• Include only lib/ folder in test coverage report

Context

N/A

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.40%. Comparing base (c15b77a) to head (ce84ef5).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1128      +/-   ##
==========================================
+ Coverage   96.28%   97.40%   +1.12%     
==========================================
  Files          52       48       -4     
  Lines        5894     5826      -68     
  Branches     1481     1477       -4     
==========================================
  Hits         5675     5675              
+ Misses        213      149      -64     
+ Partials        6        2       -4     

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