chore(funbox): increase layout_mirror difficulty to level 3 (@ShizukoV) (monkeytypegame#6761)

### Description
I've changed the difficulty of the `layout_mirror` funbox from 1 to 3.

The `layout_mirror` funbox completely mirrors the keyboard layout,
significantly increasing difficulty compared to other funboxes currently
labeled as difficulty level 1, (`earthquake`, `capitals`, `gibberish`),
which are much less disruptive.

The `layout_mirror` funbox is also similar to the `mirror` funbox (which
mirrors the screen), currently rated at difficulty level 3. Since
`layout_mirror` alters the entire keyboard layout itself, making even
basic typing extremely challenging, it makes sense for it to also be
difficulty level 3.

Author: ShizukoV

packages/funbox/src/list.ts

@@ -133,7 +133,7 @@ const list: Record<FunboxName, FunboxMetadata> = {
   layout_mirror: {
     description: "Mirror the keyboard layout",
     canGetPb: true,
-    difficultyLevel: 1,
+    difficultyLevel: 3,
     properties: ["changesLayout"],
     frontendFunctions: ["applyConfig", "rememberSettings"],
     name: "layout_mirror",