Revise CI and README

[nietras]

• Set VALIDATE_DOTNET_SLN* false as covered by separate dotnet format. Keeps failing due to not same version in super-linter docker as used for dev.
• Revise README and remove bullet points in start.
• Add after_n_builds to .codecov.yml
• Rename build to build-and-test in dotnet.yml

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.63%. Comparing base (de76335) to head (579bb20).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #256   +/-   ##
=======================================
  Coverage   99.63%   99.63%           
=======================================
  Files          54       54           
  Lines        4339     4339           
  Branches      503      503           
=======================================
  Hits         4323     4323           
  Misses         12       12           
  Partials        4        4           

Flag	Coverage Δ
Debug	99.35% <ø> (ø)
Release	99.73% <ø> (ø)
macos-latest	93.36% <ø> (ø)
ubuntu-latest	99.51% <ø> (ø)
windows-latest	99.51% <ø> (ø)

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