Add support for UnifiedSEq

[lsrcz]

These are leftovers for #211.

[codecov]

Codecov Report

Attention: Patch coverage is 45.45455% with 6 lines in your changes missing coverage. Please review.

Project coverage is 55.34%. Comparing base (ac0934b) to head (acb6bb8).

Files	Patch %	Lines
src/Grisette/Unified/Internal/Class/UnifiedSEq.hs	45.45%	5 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #212      +/-   ##
==========================================
- Coverage   55.39%   55.34%   -0.06%     
==========================================
  Files          97       97              
  Lines        7548     7555       +7     
  Branches      644      648       +4     
==========================================
  Hits         4181     4181              
- Misses       2723     2726       +3     
- Partials      644      648       +4     

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