Throttle (leading + trailing)

Implement throttle(fn, wait) such that:

• The first call fires immediately (leading edge)
• Subsequent calls within wait ms are ignored, except the last one — it fires wait ms after the last call (trailing edge)
• Forwards args + preserves this

const t = throttle((x) => log(x), 100);
t(1); t(2); t(3);
// log(1)  immediately
// log(3)  ~100ms later

Analyze: time per call, space per throttled fn.