add: more complete shell.nix

[Ben-PH]

Disclaimer: changes made under the output of an LLM

Evidently my sysconfig is missing some things. compiling, i got this error:

➜ cargo run -p cuboid
error: rustc 1.91.1 is not supported by the following packages:
  wgpu@28.0.0 requires rustc 1.92
  wgpu@28.0.0 requires rustc 1.92
  wgpu@28.0.0 requires rustc 1.92
Either upgrade rustc or select compatible dependency versions with
`cargo update <name>@<current-ver> --precise <compatible-ver>`
where `<compatible-ver>` is the latest version supporting rustc 1.91.1

The fix was to add rustup to packages (including the local dir use)

I then had this error:

     Running `target/debug/cuboid`
Error: Error displaying model

Caused by:
    0: Error initializing event loop
    1: os error at /home/ben/rust/fornjot/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/winit-0.30.13/src/platform_impl/linux/mod.rs:788: Failed to load one of xlib's shared libraries

Which was fixed with the xorg additions to libpath