Change testing framework to Microsoft Testing Platform (MTP)

[askpt]

Update the testing framework in this repository to use Microsoft Testing Platform (MTP) as described here.

• Review the current testing approach.
• Refactor and migrate tests to be compatible with MTP.
• Update documentation and CI scripts to use the new platform.
• Ensure all tests are passing after migration.
• Ensure the coverage is reported correctly.

Reference: https://learn.microsoft.com/en-us/dotnet/core/testing/microsoft-testing-platform-intro?tabs=dotnetcli

For xUnit: https://xunit.net/docs/getting-started/v3/microsoft-testing-platform