feat: add Roslyn-based compile-time request handler registration

Introduce compile-time registration capabilities with source generation, enabling automatic handler registration.

README.md

@@ -66,7 +66,29 @@ public class ScalarBehavior : IScalarRequestBehavior<ScalarRequest, string>
 }
 ```
 
+### Compile-time registration
+
+Projects that directly reference `Geekeey.Request` also get generated registration methods in the
+`Geekeey.Request` namespace:
+
+```csharp
+collection.AddRequestDispatcher(builder => builder
+  .AddExampleProject()
+  .Add(typeof(ScalarBehavior)));
+
+collection.AddRequestDispatcher(builder => builder
+  .AddExampleProject(ServiceLifetime.Scoped)
+  .Add(typeof(ScalarBehavior)));
+```
+
+- generation is enabled by default
+- disable it with `<CompiletimeRequestDispatchHandlerRegistration>false</CompiletimeRequestDispatchHandlerRegistration>`
+- rename the generated `Add<Name>(...)` methods with `CompiletimeRequestDispatchHandlerName`
+- only request handlers are generated; behaviors still need normal registration
+- nested request handlers are rejected during `Add(...)` registration, including `SearchHandlerInAssembly(...)` and by the source generator
+- use one registration style per assembly: generated methods or `SearchHandlerInAssembly(...)`
+
 ## Behaviour of the Handlers
 
-Handlers are resolved from either the DI conatiner or are created on the fly but can receive arguments from the DI
+Handlers are resolved from either the DI container or are created on the fly but can receive arguments from the DI
 container when being constructed. The same also applied for the request pipeline behaviours.