Create better HTML comment parser - Allow more semconv snippet headers.

[jsuereth]

Towards: #501

Create a more flexible HTML comment parser so we don't RELY on spaces to exist to succesfully parse HTML comments.

[codecov]

Codecov Report

Attention: Patch coverage is 91.30435% with 2 lines in your changes missing coverage. Please review.

Project coverage is 74.0%. Comparing base (c5c66ba) to head (61f6672).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/weaver_semconv_gen/src/parser.rs	91.3%	2 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main    #512   +/-   ##
=====================================
  Coverage   73.9%   74.0%           
=====================================
  Files         50      50           
  Lines       3911    3930   +19     
=====================================
+ Hits        2894    2911   +17     
- Misses      1017    1019    +2     

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[lquerel]

LGTM