Moves treefmt-nix input and configuration from the main flake to the dev partition, since it's a development-only dependency. Also switches pre-commit hooks from individual formatter hooks to the unified treefmt hook for better consistency.
(cherry picked from commit 85f10d0410a061f151722042924afc8523869aa7)
(cherry picked from commit ddf306bb9564a43fb42ab4321b390e766254f1c4)