Update bindings to 4.15

[LauraWebdev]

This has been a long time in the making, but over the coming weeks, I will implement more and more API changes from the most recent GodotSteam release into this project.

For this reason, I will close some of the older issues that will be fixed by this release.

I sadly did not have the time yet, and as with GodotSteam itself, it is hard to find people sponsor this type of work (hence me linking my Ko-Fi in the README, but after working on some other things, I found a slot of time where I can actively work on this bigger rewrite.

[LauraWebdev]

Work will be tracked in this branch: https://github.com/LauraWebdev/GodotSteam_CSharpBindings/tree/refresh-august-2025

I've used https://github.com/Delsin-Yu/CSharp-Wrapper-Generator-for-GDExtension that seems to be a good basis. Some methods don't seem to generate properly though, so I've decided to write a small patcher script that will go through the generated C# code and apply manual patches.

This also ensures that we will be able to improve developer experience with different method names / attribute types etc.