[nicknad]

Summary

This PR releases 2.0.0. The libraries target net11.0 only, which sets the language version to C# 15.

• This release removes net8.0, which reached end of support on 2026-11-10. net11.0 is the only target.
• The target framework sets the language version to C# 15. The netstandard2.0 analyzer pins 15.0 because its SDK default is C# 7.3.
• This release removes redundant Microsoft.Extensions.* package references that the net11 framework now provides.
• docs/csharp15-adoption.md records the feature inventory, the preview pilot, and the net8.0 and net11.0 measurements.
• The PR includes the statechart documentation that docs/README.md links.

Breaking changes

• The build produces no net8.0 assets. Consumers on .NET 8 must stay on 1.x.
• This release removes Microsoft.Extensions.* package dependencies where the net11 framework provides them.

Verification

• dotnet build Sparc.slnx -c Release reports 0 warnings and 0 errors.
• dotnet build Sparc.Samples.slnx -c Release reports 0 warnings and 0 errors.
• Tests pass. Unit reports 241 tests, with 232 passed and 9 Unix-only tests skipped on Windows. Concurrency passes all 5 tests, Fuzz passes all 21, and Process passes all 12.
• The public API did not change, and PublicApiAnalyzers pass.

Performance

The in-process comparison between net8.0 and net11.0 was inconclusive at a 10% minimum detectable effect on this host. The data show no regression and no speedup. The raw results, limits, and falsifiers are in docs/csharp15-adoption.md.

Notes

• This PR does not re-capture the regression baseline. A capture and the next pass differed by a factor of about 4 with no code change.