Migrates solution to .slnx format

[edumserrano]

Updates the solution file format from .sln to the more modern .slnx format.

This provides a cleaner, folder-based structure within the solution explorer and simplifies management of projects.

Also updates documentation and build scripts to reflect the solution file name change.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.02%. Comparing base (538dcd5) to head (b4081e4).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #208   +/-   ##
=======================================
  Coverage   91.02%   91.02%           
=======================================
  Files          44       44           
  Lines         479      479           
  Branches       51       51           
=======================================
  Hits          436      436           
  Misses         35       35           
  Partials        8        8           

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