Implement throttle

A scroll handler should react at once, then stay quiet until the next window opens. That is leading-edge throttle. It is not debounce: nothing should fire later on its own.

Implement throttle(fn, wait).

The first call invokes fn immediately and returns whatever fn returned. Further calls during the next wait milliseconds do nothing. They do not invoke fn, and they do not schedule a later call. After wait ms have passed since the last invocation, the next call invokes fn again.

With wait of 100:

const t = throttle((n) => n * 2, 100)
t(21) // 42, immediately
t(99) // ignored: still inside the window
// 100ms pass: fn does not run by itself
t(3)  // invokes fn again

The grader moves time on a virtual clock. setTimeout, clearTimeout, and Date.now work. Time does not pass on its own, and setInterval is not available.

Requirements:

• The first call invokes fn immediately.
• Calls during the wait window do not invoke fn.
• Once wait ms have passed since the last invocation, the next call invokes fn again.
• fn receives the arguments of the call that actually invoked it.
• On a call that invokes fn, return what fn returned.

Write a top-level function named throttle. Do not use export or module.exports.