[New Output] Support "Testing started" Output

[ikelax]

Adresses #206.

This is still a draft. I have not tested the changes yet. Also, I want to write a few unit tests for my changes.

[codecov]

Codecov Report

Attention: Patch coverage is 22.22222% with 7 lines in your changes missing coverage. Please review.

Project coverage is 78.05%. Comparing base (2e54128) to head (b4f1317).
Report is 4 commits behind head on main.

Files	Patch %	Lines
Sources/XcbeautifyLib/CaptureGroups.swift	0.00%	4 Missing ⚠️
...rces/XcbeautifyLib/Renderers/OutputRendering.swift	25.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #284      +/-   ##
==========================================
- Coverage   85.71%   78.05%   -7.67%     
==========================================
  Files          15       15              
  Lines        1645     1654       +9     
==========================================
- Hits         1410     1291     -119     
- Misses        235      363     +128     

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