ci: use crane flake to build with nix

This enables to add cargo `fmt`, `clippy` and `deny` to nix, using cached results.

Move the `teepot` crate to the `crates` subdir to make the life easier for
the `crane` flake.

Signed-off-by: Harald Hoyer <harald@matterlabs.dev>

flake.lock

@@ -1,5 +1,25 @@
 {
   "nodes": {
+    "crane": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1709610799,
+        "narHash": "sha256-5jfLQx0U9hXbi2skYMGodDJkIgffrjIOgMRjZqms2QE=",
+        "owner": "ipetkov",
+        "repo": "crane",
+        "rev": "81c393c776d5379c030607866afef6406ca1be57",
+        "type": "github"
+      },
+      "original": {
+        "owner": "ipetkov",
+        "repo": "crane",
+        "type": "github"
+      }
+    },
     "flake-compat": {
       "flake": false,
       "locked": {
@@ -287,6 +307,7 @@
     },
     "root": {
       "inputs": {
+        "crane": "crane",
         "nixpkgs": "nixpkgs",
         "nixsgx-flake": "nixsgx-flake",
         "rust-overlay": "rust-overlay",