Switch to Rust nightly for builds

[orhun]

Build is failing on the main branch due to rust-lang/rust#93706

 error[E0658]: trait bounds other than `Sized` on const fn parameters are unstable
  --> core/src/math/size.rs:16:6
   |
16 | impl<T: Num + Copy> Size<T> {
   |      ^
17 |     pub const fn new(width: T, height: T) -> Self {
   |     --------------------------------------------- function declared as const here
   |
   = note: see issue #93706 <https://github.com/rust-lang/rust/issues/93706> for more information

For more information about this error, try `rustc --explain E0658`.
error: could not compile `fishfight-core` due to previous error
Error: Process completed with exit code 101.

This PR updates the workflows and adds a Rust toolchain configuration to use nightly channel until const_fn_trait_bound is available in stable Rust.

[olefasting]

Awesome! There are some dependencies that also require nightly, when using the internal backend, IIRC, so this was probably unavoidable, any ways

[aleokdev]

I believe this has been fixed with Rust 1.61.0: https://blog.rust-lang.org/2022/05/19/Rust-1.61.0.html