mpvScripts.buildLua: Run {pre, post}install hooks

This is necessary, as users of buildLua may expect the phase hooks to work,
including indirect uses such as adding a hook through `mpvScripts.foo.override`.

pkgs/applications/video/mpv/scripts/buildLua.nix

···
     preferLocalBuild = true;
 
     outputHashMode = "recursive";
-    installPhase = "install -m644 -Dt $out/share/mpv/scripts ${scriptPath}";
-    passthru.scriptName = fileName scriptPath;
+    installPhase = ''
+      runHook preInstall
+      install -m644 -Dt $out/share/mpv/scripts ${scriptPath}
+      runHook postInstall
+    '';
 
+    passthru.scriptName = fileName scriptPath;
     meta.platforms = lib.platforms.all;
   } args)
 )