A new test project, `DigitalData.EmailProfiler.Tests`, has been added to the solution. The project is configured as a .NET 8.0 test project with xUnit as the testing framework. It includes necessary NuGet dependencies such as `coverlet.collector`, `Microsoft.NET.Test.Sdk`, and `xunit.runner.visualstudio`.
The solution file has been updated to include the new project, along with its build configurations (`Debug|Any CPU` and `Release|Any CPU`). A new solution folder, `tests`, has been added, and the test project is nested under it.
Updated Visual Studio version in the solution file to 17.14.36717.8.
Added three new projects: Infrastructure, Domain, and Application,
all targeting .NET 8.0. Enabled implicit global usings and nullable
reference types in the new projects. Updated solution configuration
and nested the new projects under the `src` folder.
