emoji_eventsMemoize with a cache limit

Write memoize(fn, limit) that returns a function which remembers results by its arguments.

• Calling it again with the same arguments returns the cached result without calling fn.
• Arguments are compared by value: use JSON.stringify(args) as the cache key.
• Keep at most limit results; when full, forget the oldest entry.
• The returned function has a .clear() method that empties the cache.

Acceptance criteria

• The tests at the bottom print All tests passed.

Hint: a Map remembers insertion order, and map.keys().next().value is the oldest key.