Update targets and dependencies for .NET 10

[Copilot]

This updates the repo to .NET 10 and rolls the package major to reflect the target/runtime shift. The change also aligns the core identity/cache dependencies and CI SDK with the new target set.

• Target frameworks

  • Move library projects from net6.0;net8.0 to net8.0;net10.0
  • Move test projects to net10.0
  • Drop the remaining net6.0 references in docs/sample output paths

• Dependency refresh

  • Bump the direct Microsoft identity/token/configuration/caching packages to current compatible versions
  • Update Microsoft.NET.Test.Sdk for the .NET 10 test projects
  • Remove obsolete ASP.NET 2.x package references from test/server projects

• ASP.NET hosting alignment

  • Replace legacy package-based ASP.NET hosting dependencies with the shared framework reference used by current SDKs

  <FrameworkReference Include="Microsoft.AspNetCore.App" />

• Build/release metadata

  • Update the GitHub Actions workflow to use a .NET 10 SDK
  • Add the 7.0.0 release note entry for the breaking target/dependency change