[chore] Move mdatagen code to internal, no public API needed

[bogdandrutu]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 76.19048% with 10 lines in your changes missing coverage. Please review.

Project coverage is 92.28%. Comparing base (d3a1718) to head (6c4ea51).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/mdatagen/internal/loader.go	66.66%	6 Missing ⚠️
cmd/mdatagen/main.go	66.66%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #11181   +/-   ##
=======================================
  Coverage   92.28%   92.28%           
=======================================
  Files         413      413           
  Lines       19761    19761           
=======================================
  Hits        18237    18237           
  Misses       1152     1152           
  Partials      372      372           

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