Add formatting, linting, and testing to CI checks (#44)

This PR adds `cargo fmt -- --check`, `nx lint ...` and `nx test ...` as
GitHub Actions. This will cause future PRs to automatically fail when
formatting issues, Clippy warnings, or test failures are present in the
changed code.

studio/src/lib.rs

@@ -16,7 +16,7 @@ mod hierarchy;
 mod input;
 mod inspector;
 mod interaction;
-mod math;
+pub mod math;
 mod mixamo;
 mod persistance;
 mod scene;