feat: use rust-overlay to get the rust binaries

This should ensure I use my own rust version instead of the one in
nixpkgs.

flake.lock

@@ -53,10 +53,31 @@
         "crane": "crane",
         "flake-parts": "flake-parts",
         "nixpkgs": "nixpkgs",
+        "rust-overlay": "rust-overlay",
         "systems": "systems",
         "treefmt-nix": "treefmt-nix"
       }
     },
+    "rust-overlay": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1747363019,
+        "narHash": "sha256-N4dwkRBmpOosa4gfFkFf/LTD8oOcNkAyvZ07JvRDEf0=",
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "rev": "0e624f2b1972a34be1a9b35290ed18ea4b419b6f",
+        "type": "github"
+      },
+      "original": {
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "type": "github"
+      }
+    },
     "systems": {
       "locked": {
         "lastModified": 1681028828,