Add tests for maui

[vb2ae]

This pull request introduces a suite of unit tests for the Caliburn.Micro.Maui project and updates the project configuration. The changes include adding new test classes, updating the project file to include necessary packages and settings, and modifying access levels in the ActionMessage class.

Unit Tests Addition:

• ActionMessageTests: Added tests to verify the MethodName, Handler, and Parameters properties of ActionMessage. (src/Caliburn.Micro.Maui.Tests/ActionMessageTests.cs)
• AssemblyCacheTests: Added tests to ensure adding the same assembly multiple times and resetting the cache does not throw exceptions. (src/Caliburn.Micro.Maui.Tests/AssemblyCacheTests.cs)
• FormsPlatformProviderTests: Added tests to verify the behavior of FormsPlatformProvider methods. (src/Caliburn.Micro.Maui.Tests/FormsPlatformProviderTests.cs)

Project Configuration:

• Caliburn.Micro.Maui.Tests.csproj: Created a new test project file with references to necessary packages and project dependencies. (src/Caliburn.Micro.Maui.Tests/Caliburn.Micro.Maui.Tests.csproj)
• Caliburn.Micro.Maui.csproj: Updated the language version to 10.0 and added an InternalsVisibleTo attribute for the test project. (src/Caliburn.Micro.Maui/Caliburn.Micro.Maui.csproj) [1] [2]

Codebase Changes:

• ActionMessage.cs: Changed the access level of the Handler property setter from private to internal. (src/Caliburn.Micro.Platform/Platforms/Maui/ActionMessage.cs)

These changes collectively enhance the test coverage for the Caliburn.Micro.Maui project and ensure that the project is configured correctly for testing.

Closes #877