Add customizable tree rendering styles

[santisq]

New Features

• Added support for customizable tree rendering styles via the new RenderingStyle property on TreeStyle:
  • Available styles: Fancy (default), FancyRounded, Classic, ClassicRounded.
  • Modern Unicode box-drawing styles and traditional ASCII styles are now supported.

Changed

• Updated about_TreeStyle.md documentation to cover the new rendering style options.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.18%. Comparing base (e18f82d) to head (7201cf6).
⚠️ Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #65      +/-   ##
==========================================
+ Coverage   98.16%   98.18%   +0.01%     
==========================================
  Files          37       37              
  Lines         819      825       +6     
  Branches      107      108       +1     
==========================================
+ Hits          804      810       +6     
  Misses          8        8              
  Partials        7        7              

Flag	Coverage Δ
PS-5.1	97.68% <100.00%> (+0.01%)	⬆️
PS-7_Linux	71.49% <60.00%> (+0.33%)	⬆️
PS-7_Windows	97.29% <100.00%> (+0.02%)	⬆️

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