add psalm check

checks/phpstan.nix

@@ -0,0 +1,31 @@
+{
+  composerMeta,
+  src,
+  phpstan,
+  vendor,
+  stdenvNoCC,
+}: let
+  inherit (composerMeta) version name;
+in
+  stdenvNoCC.mkDerivation {
+    inherit src version;
+    pname = "${name}-phpstan";
+
+    nativeBuildInputs = [phpstan];
+
+    postPatch = ''
+      ln -s ${vendor}/vendor vendor
+    '';
+
+    buildPhase = ''
+      runHook preBuild
+
+      phpstan analyse
+
+      runHook postBuild
+    '';
+
+    installPhase = ''
+      touch $out
+    '';
+  }