feat(funbox): Add rot13 funbox (@Leonabcd123) (#7116)

### Description

Added a new funbox mode that implements the rot13 cipher, shifting each
character over by 13 places.

I'm not really sure which properties fit best with this...

Implements #6565

frontend/src/ts/test/funbox/funbox-functions.ts

@@ -332,6 +332,30 @@ const list: Partial<Record<FunboxName, FunboxFunctions>> = {
       return randomcaseword;
     },
   },
+  rot13: {
+    alterText(word: string): string {
+      let alphabet = "abcdefghijklmnopqrstuvwxyz";
+
+      let rot13Word = "";
+
+      for (let ch of word) {
+        let chIndex = alphabet.indexOf(ch.toLowerCase());
+        if (chIndex === -1) {
+          rot13Word += ch;
+          continue;
+        }
+
+        let rot13Ch = (chIndex + 13) % 26;
+        if (ch.toUpperCase() === ch) {
+          rot13Word += alphabet[rot13Ch]?.toUpperCase();
+        } else {
+          rot13Word += alphabet[rot13Ch];
+        }
+      }
+
+      return rot13Word;
+    },
+  },
   backwards: {
     alterText(word: string): string {
       return word.split("").reverse().join("");

packages/funbox/src/list.ts

@@ -460,6 +460,14 @@ const list: Record<FunboxName, FunboxMetadata> = {
     name: "asl",
     cssModifications: ["words"],
   },
+  rot13: {
+    description: "Vg znl abg or frpher, ohg vg vf sha gb glcr!",
+    canGetPb: true,
+    difficultyLevel: 1,
+    properties: [],
+    frontendFunctions: ["alterText"],
+    name: "rot13",
+  },
   no_quit: {
     description: "You can't restart the test.",
     canGetPb: true,

packages/schemas/src/configs.ts

@@ -304,6 +304,7 @@ export const FunboxNameSchema = z.enum([
   "ALL_CAPS",
   "polyglot",
   "asl",
+  "rot13",
   "no_quit",
 ]);
 export type FunboxName = z.infer<typeof FunboxNameSchema>;