checks: Add formatting, statix and deadnix checks

flake-parts/checks.nix

@@ -0,0 +1,20 @@
+{ inputs, self, ... }:
+{
+  perSystem =
+    { inputs', pkgs, ... }:
+    {
+      checks = {
+        formatting = (inputs.treefmt.lib.evalModule pkgs "${self}/treefmt.nix").config.build.check self;
+
+        statix = pkgs.runCommand "statix" { buildInputs = [ inputs'.statix.packages.statix ]; } ''
+          statix check ${self}
+          touch $out
+        '';
+
+        deadnix = pkgs.runCommand "deadnix" { buildInputs = [ pkgs.deadnix ]; } ''
+          deadnix --fail ${self}
+          touch $out
+        '';
+      };
+    };
+}