chore: add treefmt - to format them all

- this is a unified & modern approch to keeping all files according to fmt-spec
- has excellent editor integration

flake.lock

@@ -21,6 +21,21 @@
         "type": "github"
       }
     },
+    "flake-utils": {
+      "locked": {
+        "lastModified": 1610051610,
+        "narHash": "sha256-U9rPz/usA1/Aohhk7Cmc2gBrEEKRzcW4nwPWMPwja4Y=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "3982c9903e93927c2164caa727cd3f6a0e6d14cc",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
     "flakeCompat": {
       "flake": false,
       "locked": {
@@ -73,7 +88,8 @@
         "fenix": "fenix",
         "flakeCompat": "flakeCompat",
         "flakeUtils": "flakeUtils",
-        "nixpkgs": "nixpkgs"
+        "nixpkgs": "nixpkgs",
+        "treefmt": "treefmt"
       }
     },
     "rust-analyzer-src": {
@@ -92,6 +108,27 @@
         "repo": "rust-analyzer",
         "type": "github"
       }
+    },
+    "treefmt": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1640364438,
+        "narHash": "sha256-sV1Oa9JVNmpAwZ4cnVs7ovHrKL8EPg3J08jPX/a48LI=",
+        "owner": "numtide",
+        "repo": "treefmt",
+        "rev": "26d7f5f15e5d22d4413ba7c5ae0447fdc0b5cc76",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "treefmt",
+        "type": "github"
+      }
     }
   },
   "root": "root",