feat(NODE-6296)!: remove cursor default batch size of 1000

[baileympearson]

Description

Summary of Changes

Cursors no longer provide a default batchSize of 1000 for getMores.

Notes for Reviewers

What is the motivation for this change?

Release Highlight

Cursors no longer provide a default batchSize of 1000 for getMores

In driver versions <7.0, the driver provides a default batchSize of 1000 for each getMore when iterating a cursor. This behavior is not ideal because the default is set regardless of the documents being fetched. For example, if a cursor fetches many small documents, the driver's default of 1000 can result in many round-trips to fetch all documents, when the server could fit all documents inside a single getMore if no batchSize were set.

Now, cursors no longer provide a default batchSize when executing a getMore. A batchSize will only bet set on getMore commands if a batchSize has been explicitly configured for the cursor.

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[durran]

Waiting on CI, perf tests timed out and rerunning.