fix(NODE-6242): close becomes true after calling close when documents still remain

[nbbeeken]

Description

What is changing?

Fix a change in behavior to close introduced in a recent cursor refactor. The expectation was that close became true when no more documents remain locally.

Is there new documentation needed for these changes?

Yes, API docs updated.

What is the motivation for this change?

The closed flag is used to determine if there are docs remaing in mongosh

Release Highlight

Clarified cursor state properties

The cursor has a few properties that represent the current state from the perspective of the driver and server. This PR corrects an issue that never made it to a release but we would like to take the opportunity to re-highlight what each of these properties mean.

• cursor.closed - cursor.close() has been called, and there are no more documents stored in the cursor.
• cursor.killed - cursor.close() was called while the cursor still had a non-zero id, and the driver sent a killCursors command to free server-side resources
• cursor.id == null - The cursor has yet to send it's first command (ex. find, aggregate)
• cursor.id.isZero() - The server sent the driver a cursor id of 0 indicating a cursor no longer exists on the server side because all data has been returned to the driver.
• cursor.bufferedCount() - The amount of documents stored locally in the cursor.

Double check the following

• Ran npm run check:lint script
• Self-review completed using the steps outlined here
• PR title follows the correct format: type(NODE-xxxx)[!]: description
  • Example: feat(NODE-1234)!: rewriting everything in coffeescript
• Changes are covered by tests
• New TODOs have a related JIRA ticket