feat: add devshell and improve input handling of cells

pass system to cells and their flake.nix inputs

cells/repo/devShells.nix

@@ -0,0 +1,7 @@
+{inputs, ...}: let
+  inherit (inputs) pkgs devshellLib;
+in {
+  default = devshellLib.mkShell {
+    packages = [pkgs.alejandra];
+  };
+}

cells/repo/flake.lock

@@ -0,0 +1,28 @@
+{
+  "nodes": {
+    "devshell": {
+      "locked": {
+        "dir": "lib",
+        "lastModified": 1753958239,
+        "narHash": "sha256-J0B5rfQAza9UKSqnKINn++AsrMWxG3/oTqVUt3QRlWk=",
+        "owner": "rensa-nix",
+        "repo": "devshell",
+        "rev": "fbacfc149b59acf68efa97951418a9a7a7022707",
+        "type": "gitlab"
+      },
+      "original": {
+        "dir": "lib",
+        "owner": "rensa-nix",
+        "repo": "devshell",
+        "type": "gitlab"
+      }
+    },
+    "root": {
+      "inputs": {
+        "devshell": "devshell"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

cells/repo/flake.nix

@@ -0,0 +1,14 @@
+{
+  inputs = {
+    devshell.url = "gitlab:rensa-nix/devshell?dir=lib";
+  };
+
+  outputs = i:
+    i
+    // rec {
+      pkgs = import i.parent.nixpkgs {
+        inherit (i) system;
+      };
+      devshellLib = i.devshell.lib {inherit pkgs;};
+    };
+}

cells/test/test.nix

@@ -1,6 +1,3 @@
 {
-  inputs,
-  cell,
-}: {
   hello = "world";
 }