Add Nim GDExtension

[xix-xeaon]

I've been testing the extension for a few different things which have worked well and it has an active developer so I think it can be added to the list.

[tetrapod00]

Approval in theory. Someone from GDExtension needs to confirm that is considered well-developed enough to be added.

[dsnopek]

Someone from GDExtension needs to confirm that is considered well-developed enough to be added.

I don't know that anyone on the GDExtension team has directly used the Nim binding, and the developer hasn't (to my knowledge) been in contact with the team either. Given that I don't personally know Nim, and the binding itself is written in Nim (as opposed to being written in C or C++, which sometimes is the case), it's hard to review it. :-)

Poking around on GitHub, it appears the current Nim binding is a continuation of this project, which has been around since May 2023. The two projects have 58 and 73 stars, respectively. That's smaller than the Nim GDNative bindings for Godot 3 which goes back many more years and has ~500 stars, but that still seems fairly promising to me?

I'd probably err on the side of including it.

[mhilbrunner]

Merged. Thanks and congrats on your first merged contribution!