feat: add nix-shell file for nvidia

[The-personified-devil]

Closes #2337

Easy to use + low code complexity solution to be able to build alvr with nvidia support on linux for distros that have issues with cuda. Note that this currently is only supposed to supplement an environment that already provides rust and a couple other necessary things, not present a full build environment (should this be changed?). It'll also need to be documented on the wiki and should hopefully replace some more manual and unreliable methods of installing cuda featured there.

[failboat78]

I get errors when trying to build using this.

The prepare-deps stage works ok - which was the part that was failing on arch. But the build-streamer step fails with errors relating to alsa and openssl.

error: failed to run custom build command for openssl-sys v0.9.102 error: failed to run custom build command for alsa-sys v0.3.1

[The-personified-devil]

Since nixos has fixed their packaging for alvr, we should probably base this change on that since it's already a lot more complete. Same goes for #2402.

Also, a more medium-term goal is to move away from ffmpeg, since it's arguably just a mess, and to replace it with direct support for vulkan video encoding (widespread support is available from mesa 25 on). This would fully replace the intent of this pr, although I'm still interested in providing first-party integration with nix.