Add protocol tests and CI coverage enforcement

[c3rebro]

Summary

• add reusable fake reader transport plus protocol and feature-flag regression tests
• document Legic/MIFARE edge cases and flesh out helper APIs used by the tests
• wire up CI to run the test suite with coverage enforcement on pushes and pull requests

Testing

• dotnet test Elatec.NET.sln /p:CollectCoverage=true /p:CoverletOutputFormat=cobertura /p:Threshold=5 /p:ThresholdType=line /p:ThresholdStat=total

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Codex Task