Modernize Imp for .NET 8 and .NET 10

[MikeChristensen]

Summary

• target the supported .NET 8 and .NET 10 LTS releases
• replace legacy ASP.NET Core 2.2 and log4net packages with the ASP.NET Core shared framework and standard ILogger integration
• add multi-targeted real-Kestrel integration tests and clean package-consumer validation
• fail restores on vulnerable dependencies and add Dependabot maintenance
• prepare project, CI, and release metadata for Imp 0.2.0
• update the README; corresponding Wiki documentation is already published

Compatibility

This intentionally drops .NET Standard 2.0 and ASP.NET Core 2.x support. Existing UseImp, page, template, postback, routing, and configuration behavior remains unchanged. The existing two-argument ImpMiddleware constructor is retained for compatibility.

Validation

• .NET 10: 11 tests passed
• .NET 8 SDK container: 8 Imp tests passed
• packed KitchenPC.Imp 0.2.0 consumed successfully by clean .NET 8 and .NET 10 web projects
• Imp package has no ordinary NuGet dependencies
• NuGet vulnerability audit reports no vulnerable packages
• package contents and release-version validation verified

After this merges and builds successfully, the intended release tag is v0.2.0.