Fixes for canonical(), __repr__, and specificity().

[wRAR]

1. Selector.canonical() silently drops the :has() combinator
2. More canonical() outputs that are wrong or unparseable
3. Matching/SpecificityAdjustment ignore the base selector's specificity (Fixes The specificity computation is wrong for :where and :is #136)
4. Relation.canonical()/specificity() have dead subselector[…] branches

Found and fixed by an LLM, all test cases validated manually.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.73%. Comparing base (743c6e5) to head (68b38e9).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #169      +/-   ##
==========================================
+ Coverage   96.61%   96.73%   +0.12%     
==========================================
  Files           3        3              
  Lines         885      918      +33     
  Branches      136      149      +13     
==========================================
+ Hits          855      888      +33     
  Misses         14       14              
  Partials       16       16              

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