chore(nix): update flake dependencies (#179)

### TL;DR
Updated dependencies in flake.lock to their latest versions and removed nixpkgs-stable input.

### What changed?
- Updated git-hooks.nix from `f0f0dc4` to `a5a961387`
- Updated nixpkgs from `edf04b7` to `cbd8ec4`
- Updated treefmt-nix from `56c0ecd` to `1788ca5`

### How to test?
1. Run `nix flake update` to verify the lock file updates correctly
2. Build and test the project to ensure all dependencies work with the new versions
3. Verify that removing nixpkgs-stable doesn't affect any functionality

### Why make this change?
Keeping dependencies up to date ensures we have the latest bug fixes, security patches, and features.