Port performance heavy parts of code to C#, while leveraging GDScript for scripting.

[dnesov]

Since Godot's .NET supported is in place, there's no need to use C++ through GDExtension for parts that require maintainability and performance. It makes sense to go with C# as it offers much better tooling and developer experience, with performance levels that should meet the requirements of the project.

Going further, all features that were planned to be implemented in C++ (like room generation) will be worked on in C#, with GDScript still being a primary language for content like items, status effects, or UI.