Implement Throttle

Write throttle(fn, wait): the returned function calls fn at most once per wait ms.

const onScroll = throttle(update, 100);
// calls at 0, 30 and 60 ms  ->  update runs at 0 (with the first call's arguments)
//                               and at 100 (with the call at 60's arguments)

Rules

• The first call fires immediately.
• Calls inside the window collapse into one trailing fire at the window's end, with the latest arguments; that fire starts the next window.
• A call after a quiet window fires immediately again.
• Return a real function, not an arrow, so a caller's this is forwarded.

The grader replays timed call scripts on a virtual clock — setTimeout, clearTimeout, and Date.now are stubbed — so build on those, not on performance.now or promises. Each case's input is the wait and a script of [ms, "call", ...args] steps; the expected output lists every fire as {at, args}.