feat(NODE-7121): prevent connection churn on backpressure errors when establishing connections

[baileympearson]

Description

Summary of Changes

This PR adopts the backpressure changes from mongodb/specifications#1860 and mongodb/specifications#1855.

Notes for Reviewers

What is the motivation for this change?

Release Highlight

Release notes highlight

Double check the following

• Lint is passing (npm run check:lint)
• 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
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[baileympearson]

Typescript wasn't properly inferring the types after command.bind() is called for some reason. After adjusting it to call command directly, I got a compiler error and had to provide a timeout context.

[baileympearson]

Sorry for the large diff here, reviewers. Our test runner's old mocks were too permissive and allowed tests to pass that should have failed. I've adjusted this mocking logic:

• if we need to stub before handshake errors, I create stubs that provide the bare minimum needed for the actual handshake to fail. In practice, this means stubbing net.createConnection().
• otherwise, I use rely on the old stub logic.

I've also adjusted the code to use switch statements instead of if-statements when switching on discriminated union fields, because TS errors if we haven't exhausted all switch statements.

[tadjik1]

Suggested change

	expect(checkoutFailedEvents.length).to.be.greaterThan(10);
	expect(checkoutFailedEvents.length).to.be.at.least(10);

According to the spec "Assert that at least 10 ConnectionCheckOutFailedEvent occurred."

[tadjik1]

It seems using microTask queue won't affect the functionality but it will help us later (less refactoring and unexpected failures)

Suggested change

	process.nextTick(() => socket.emit('connect'));
	queueMicrotask(() => socket.emit('connect'));