feat: Splits Server in Core and Application (#1806)

> [!Note]
> **Developer Note**
> Now developers will only need to build/run the Application project instead of everything.
> When adding new projects, make sure to: 
> 1. Add a reference to that project in the Application project.
> 2. Add the dll file to the Distribution/Data/assemblies.json file

### Summary
- Adds an application project
- Consolidates process restarts to use `Core.Kill(true)`
- Removes some old messaging, for example processor optimization
- Fixes missing build cleanup

Projects/Server.Tests/Fixtures/ServerFixture.cs

@@ -1,5 +1,7 @@
 using System;
+using System.Diagnostics;
 using System.Reflection;
+using System.Threading;
 
 namespace Server.Tests;
 
@@ -8,14 +10,14 @@ internal class ServerFixture : IDisposable
     // Global setup
     static ServerFixture()
     {
-        Core.Assembly = Assembly.GetExecutingAssembly(); // Server.Tests.dll
+        Core.ApplicationAssembly = Assembly.GetExecutingAssembly(); // Server.Tests.dll
 
         // Load Configurations
         ServerConfiguration.Load(true);
 
         // Load an empty assembly list into the resolver
         ServerConfiguration.AssemblyDirectories.Add(Core.BaseDirectory);
-        AssemblyHandler.LoadAssemblies(new[]{ "ModernUO.dll" });
+        AssemblyHandler.LoadAssemblies(["Server.dll"]);
 
         Core.LoopContext = new EventLoopContext();
         Core.Expansion = Expansion.EJ;