Enqueue collections of events instead of individual events in `MacWatchKey`?

[sungshik]

Events are enqueued to the list of pending events individually in MacWatchKey. It might be faster to, before enqueueing, collect all events that are available at that point (but not yet enqueued) and enqueue the collection. Note: This is an optimization of which the need/effectiveness currently is unclear.

Further background:

• Original comment
• In a previous version of the library, the poller used to submit a separate job to the thread pool for each incoming event. This didn't work well in situations with many events (e.g., in the torture tests). Currently, instead, the poller collects multiple events in each job. This feature of the poller might be strengthened by using "pre-collection" as suggested in this issue (or it might not; that's to be found out).