flake: add treefmt, reorganize flake, format using treefmt

flake.lock

@@ -16,9 +16,59 @@
         "type": "github"
       }
     },
+    "nixpkgs_2": {
+      "locked": {
+        "lastModified": 1719690277,
+        "narHash": "sha256-0xSej1g7eP2kaUF+JQp8jdyNmpmCJKRpO12mKl/36Kc=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "2741b4b489b55df32afac57bc4bfd220e8bf617e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "root": {
       "inputs": {
-        "nixpkgs": "nixpkgs"
+        "nixpkgs": "nixpkgs",
+        "systems": "systems",
+        "treefmt": "treefmt"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "id": "systems",
+        "type": "indirect"
+      }
+    },
+    "treefmt": {
+      "inputs": {
+        "nixpkgs": "nixpkgs_2"
+      },
+      "locked": {
+        "lastModified": 1719887753,
+        "narHash": "sha256-p0B2r98UtZzRDM5miGRafL4h7TwGRC4DII+XXHDHqek=",
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "rev": "bdb6355009562d8f9313d9460c0d3860f525bc6c",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "type": "github"
       }
     }
   },