chore(front-matter): remove regexp m flags

[timreichen]

This PR restructures regexps by removing m flags and adding capturing groups for data and body. This makes match post processing in extractAndParse() and pre processing in recognize() obsolete.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.09%. Comparing base (8c38d9c) to head (6e3f501).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6393      +/-   ##
==========================================
+ Coverage   96.08%   96.09%   +0.01%     
==========================================
  Files         560      560              
  Lines       42337    42345       +8     
  Branches     6382     6381       -1     
==========================================
+ Hits        40681    40693      +12     
+ Misses       1616     1613       -3     
+ Partials       40       39       -1     

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