Refactor Catch2 3rdparty usage

[fspindle]

• Detect if Catch2 is available from system (default)
• If not available build from embedded source

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.19%. Comparing base (5fcc8a5) to head (2881395).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1933      +/-   ##
==========================================
- Coverage   48.36%   48.19%   -0.17%     
==========================================
  Files         532      532              
  Lines       69334    69065     -269     
  Branches    32440    32304     -136     
==========================================
- Hits        33530    33288     -242     
- Misses      31519    31647     +128     
+ Partials     4285     4130     -155     

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