move modules/squashfs.nix into outputs/

modules/outputs/squashfs.nix

@@ -0,0 +1,20 @@
+{
+  config,
+  pkgs,
+  lib,
+  ...
+}:
+let
+  inherit (pkgs) liminix;
+  inherit (lib) mkIf;
+in
+{
+  config = mkIf (config.rootfsType == "squashfs") {
+    system.outputs.rootfs =
+      liminix.builders.squashfs config.filesystem.contents;
+    kernel.config = {
+      SQUASHFS = "y";
+      SQUASHFS_XZ = "y";
+    };
+  };
+}