flake.nix,flake.lock: prepare rust environment

flake.lock

@@ -2,11 +2,11 @@
   "nodes": {
     "nixpkgs": {
       "locked": {
-        "lastModified": 1755082269,
-        "narHash": "sha256-Ix7ALeaxv9tW4uBKWeJnaKpYZtZiX4H4Q/MhEmj4XYA=",
+        "lastModified": 1766314097,
+        "narHash": "sha256-laJftWbghBehazn/zxVJ8NdENVgjccsWAdAqKXhErrM=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "d74de548348c46cf25cb1fcc4b74f38103a4590d",
+        "rev": "306ea70f9eb0fb4e040f8540e2deab32ed7e2055",
         "type": "github"
       },
       "original": {
@@ -17,7 +17,28 @@
     },
     "root": {
       "inputs": {
-        "nixpkgs": "nixpkgs"
+        "nixpkgs": "nixpkgs",
+        "rust-overlay": "rust-overlay"
+      }
+    },
+    "rust-overlay": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1766371695,
+        "narHash": "sha256-W7CX9vy7H2Jj3E8NI4djHyF8iHSxKpb2c/7uNQ/vGFU=",
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "rev": "d81285ba8199b00dc31847258cae3c655b605e8c",
+        "type": "github"
+      },
+      "original": {
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "type": "github"
       }
     }
   },