fix(Interceptor): wrap the "once" event listener, ditch "untilIdle" Promise

Follow-up to #427

Changes

These are internal changes and have no effect on the public API.

This change drops the internal implementation of AsyncEventEmitter used to await all request listeners from being done. Instead, it introduces a RequestConrtoller that just holds a response Promise to whichever surface calling .respondWith().

The request listener await logic is achieved by:

Adding a once request listener that always responds to the intercepted request with `undefined. using the request controller. This leverages the native listeners execution order to provide a fall-safe listener in case the consumer hasn't handled the request in any way.
Adding a new emitAsync utility to account for async request listeners. emitAsync executes all the listeners for the given events awaiting them (i.e. in order).

mswjs / interceptors

fix(Interceptor): wrap the "once" event listener, ditch "untilIdle" Promise #430

Changes

Released: v0.25.2 🎉