Standardize lts/ghc-9.0.x to use haskell-make-package-set
Standardize lts/ghc-9.0.x to use haskell-make-package-set and modern flake structure.
Changes
- Use haskell-make-package-set.flakeModule
- Move configuration to nix/ directory
- Use horizon-ghc's lib.compilerConfig for GHC core libraries
- Remove develop/ and configuration/ directories
- Update README with correct tool versions and markdown links
- Configure treefmt to exclude generated files
Benefits
- Single source of truth for GHC core libraries (from horizon-ghc)
- Consistent structure across all LTS branches
- Modern tooling (omnix, treefmt)
- Better documentation