emit nullopt for unmatched groups in std_regex_provider::regex_search

[metsw24-max]

Noticed regex_search only pushes capture groups whose submatch participated, while create_component_match_result maps the returned vector onto the group name list by position. An optional group that does not match (e.g. pathname (a)?(b) against b) drops a slot, so b is reported under name "0" instead of "1" and group "1" disappears. Push nullopt for non-participating groups so undefined groups stay aligned with their names. The harness already skips WPT cases with null group values, which is why this was not caught.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 59.87%. Comparing base (d421a79) to head (3205011).

Files with missing lines	Patch %	Lines
src/url_pattern_regex.cpp	0.00%	0 Missing and 1 partial ⚠️

❌ Your patch check has failed because the patch coverage (0.00%) is below the target coverage (80.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1148      +/-   ##
==========================================
- Coverage   59.88%   59.87%   -0.01%     
==========================================
  Files          37       37              
  Lines        6132     6133       +1     
  Branches     2977     2978       +1     
==========================================
  Hits         3672     3672              
  Misses        617      617              
- Partials     1843     1844       +1     

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