PYTHON-5528 Add exponential backoff to operation retry loop for server overloaded errors

[blink1073]

PYTHON-5528

Summary

Adds unified and prose tests from mongodb/specifications#1862

Changes in this PR

• Unified tests added
• Unified tests passing
• Handshake prose test implemented
• Backpressure prose test implemented

Testing Plan

Added unified and prose tests, testing as part of PR.

Screenshots (optional)

N/A

Checklist

Checklist for Author

• Did you update the changelog (if necessary)?
• Is the intention of the code captured in relevant tests?
• If there are new TODOs, has a related JIRA ticket been created?

Checklist for Reviewer {@primary_reviewer}

• Does the title of the PR reference a JIRA Ticket?
• Do you fully understand the implementation? (Would you be comfortable explaining how this code works to someone else?)
• Have you checked for spelling & grammar errors?
• Is all relevant documentation (README or docstring) updated?

Focus Areas for Reviewer (optional)