Refactor jet pointer and environment handling in Rust generation #3

Job	Run time
codespell	16s
build (c, macos-latest, nixos-25.05)	3m 3s
build (c, ubuntu-latest, nixos-25.05)	1m 2s
build (c, macos-latest, nixpkgs-unstable)	3m 2s
build (c, ubuntu-latest, nixpkgs-unstable)	59s
build (haskell, macos-latest, nixos-25.05)	36m 6s
build (haskell, ubuntu-latest, nixos-25.05)	24m 4s
build (haskell, ubuntu-latest, nixpkgs-unstable)	25m 46s
build (haskell, macos-latest, nixpkgs-unstable)	25m 36s
	1h 59m 54s

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