Update repository

[olstakh]

This pull request modernizes the build and test infrastructure for the repository by upgrading to .NET 10, updating several dependencies, and transitioning from legacy Visual Studio solution files to the new .slnx format. It also updates test project configurations and improves test isolation. Below are the most important changes:

Build and SDK Upgrades

• Upgraded the .NET SDK version from 9.0 to 10.0 in global.json, and updated MSBuild SDKs to newer versions.
• Changed the target framework for all relevant projects and sample projects from net9.0 to net10.0. [1] [2] [3]
• Updated the System.Text.Json package to version 10.0.0 in Directory.Packages.props and removed redundant package references from sample projects. [1] [2]

Solution and Project Structure Modernization

• Removed legacy .sln solution files (ReferenceProtector.sln, samples/Samples.sln) and replaced them with new .slnx solution files (ReferenceProtector.slnx, samples/Samples.slnx) for improved organization and compatibility with modern tooling. [1] [2] [3] [4]

Test Infrastructure Updates

• Switched test projects to use the xunit.v3.mtp-v2 test runner, removing older xUnit and Visual Studio test runner dependencies. [1] [2] [3]
• Added a test.runner configuration for Microsoft.Testing.Platform in global.json to standardize test execution.

Build System Improvements

• Added <DisableTransitiveProjectReferences>true</DisableTransitiveProjectReferences> to central build properties to control transitive project reference behavior.
• Ensured the output path for _ReferenceProtector_DeclaredReferences.tsv in ReferenceProtector.targets is always an absolute path for reliability.

Test Isolation Enhancements

• In test setup, now creates an empty Directory.Packages.props in test directories to decouple tests from the repo's central package management settings, and explicitly sets DisableTransitiveProjectReferences to false for test builds. [1] [2]