110Implement a resilient polling engine with exponential backoff, visibility awareness, timeout, and cancellation

A naive setInterval(fetchStatus, 2000) overlaps slow requests, hammers a failing server, and keeps polling in background tabs. Implement createPoller(task, options) returning { start(), stop(), isRunning }:

• task({ signal }) is async; its result goes to onData(result), its error to onError(error).
• No overlap: the next call starts only after the previous one finished plus a delay.
• Backoff: after a success, wait interval; after the n-th consecutive failure, wait min(maxInterval, interval * backoffFactor ** n). Report every chosen delay with onSchedule(delay).
• Timeout: abort a call that runs longer than timeout ms (its signal aborts with a TimeoutError), count it as a failure and continue, even if the task ignores the signal.
• Visibility: visibility is { isHidden(), onChange(callback) → unsubscribe }. Do not start calls while hidden. When the page becomes visible again, poll immediately.
• Cancellation: stop() aborts the in-flight call, cancels any wait, and guarantees no further calls or callbacks.

Defaults: interval = 1000, maxInterval = 30000, backoffFactor = 2, timeout = 10000, onData, onError and onSchedule no-ops, and visibility based on document.visibilityState.