Use flake compat to provide the nix flakes dev shell to non flake users (#2926)

* Use flake compat to provide the nix flakes dev shell to non flake users

* Move shell.nix to .nix sub folder

.nix/flake.lock

@@ -1,5 +1,19 @@
 {
   "nodes": {
+    "flake-compat": {
+      "locked": {
+        "lastModified": 1733328505,
+        "narHash": "sha256-NeCCThCEP3eCl2l/+27kNNK7QrwZB1IJCrXfrbv5oqU=",
+        "rev": "ff81ac966bb2cae68946d5ed5fc4994f96d0ffec",
+        "revCount": 69,
+        "type": "tarball",
+        "url": "https://api.flakehub.com/f/pinned/edolstra/flake-compat/1.1.0/01948eb7-9cba-704f-bbf3-3fa956735b52/source.tar.gz"
+      },
+      "original": {
+        "type": "tarball",
+        "url": "https://flakehub.com/f/edolstra/flake-compat/1.tar.gz"
+      }
+    },
     "flake-utils": {
       "inputs": {
         "systems": "systems"
@@ -52,6 +66,7 @@
     },
     "root": {
       "inputs": {
+        "flake-compat": "flake-compat",
         "flake-utils": "flake-utils",
         "nixpkgs": "nixpkgs",
         "nixpkgs-unstable": "nixpkgs-unstable",