Excessive number of open cursors

[piotrlg9]

Current change event loop probably leads to many cursor objects being created and left for GC - this can lead to performance issues (it's not a memory leak per se, but it generates unwanted objects).

Example:

• after few minues number of MongoChangeStreamCursorImpl objects is 1274 (this should be equal to number of partitions)

Current loop scheme (MongoChangeStreamWorker.run):

        do {
            try (var cursor = changeStream.cursor()) { // constant re-creation of cursor
                ChangeStreamDocument<Document> document = cursor.tryNext();
                if (document != null) {
                //... section A
                }
       } while (true);

This code in "section A" handles just one document and then worker re-creates the cursor.

Cursor re-creation may be required but should be limited by some integer counter or time limit (e.g. re-create after n nulls returned by tryNext calls or after m milliseconds whatever goes first.