Fix underlying slice by providing a new one

When we read off the queue.read slice, it essentially pops the first
available element by doing this:

case eh.ch <- eh.queue.read[0]:
        eh.queue.read[0] = Event{}
	eh.queue.read = eh.queue.read[1:]

So the entry where the event used to exist has been overwritten with a
fresh instance of Event which will avoid a memory leak. However the
issue is that the underlying slice keeps growing. During a long running
test the slice could grow to an unnecessarily length.

To avoid this issue, when queue.read is empty and is swapped with
queue.write, just before swapping them around the existing queue.read
is overwritten with a new slice, freeing up the old potentially long
slice. This should help avoid memory leaks.

js/modules/k6/browser/common/event_emitter.go

@@ -136,6 +136,8 @@ func (e *BaseEventEmitter) emit(event string, data any) {
 		// the read queue until that is again depleted.
 		if len(eh.queue.read) == 0 {
 			eh.queue.writeMutex.Lock()
+			// Clear the read slice before swapping to prevent keeping references
+			eh.queue.read = make([]Event, 0)
 			eh.queue.read, eh.queue.write = eh.queue.write, eh.queue.read
 			eh.queue.writeMutex.Unlock()
 		}