Fix some :is(), :where() and :matches() bugs.

[wRAR]

1. :is(a,b) mangle the argument after a comma not followed by whitespace
2. :is(*, X) drops the universal argument and becomes over-restrictive
3. :is(:has(X)) translates to a never-matching garbage predicate
4. Unclosed :is( escapes as RuntimeError, not SelectorSyntaxError
5. :matches() isn't tested
6. A ns|* argument of :is()/:where()/:not() becomes a never-matching literal name test (fixes Incorrect use of XPath name() function #18)
7. name()-literal comparisons don't match node-test semantics under a default namespace

Also applies to :matches (alias for :is) and for :where (shares the implementation with :is).

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 96.83%. Comparing base (743c6e5) to head (810101e).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #167      +/-   ##
==========================================
+ Coverage   96.61%   96.83%   +0.22%     
==========================================
  Files           3        3              
  Lines         885      886       +1     
  Branches      136      136              
==========================================
+ Hits          855      858       +3     
  Misses         14       14              
+ Partials       16       14       -2     

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