PYTHON-1894: Client-side errors in in-progress transactions must not change transaction state

[sophiayangDB]

PYTHON-1894

Changes in this PR

Transactions are only advanced from STARTING -> IN_PROGRESS after the first operation reaches the server response stage. This means that client-side errors do not advance state.

Test Plan

Removed the temporary unified test skips and expected failures for this case.

Checklist

Checklist for Author

• Did you update the changelog (if necessary)?
• Is there test coverage?
• Is any followup work tracked in a JIRA ticket? If so, add link(s).

Checklist for 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?)
• Is all relevant documentation (README or docstring) updated?

[codecov-commenter]

Codecov Report

❌ Patch coverage is 93.75000% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pymongo/asynchronous/client_session.py	83.33%	0 Missing and 1 partial ⚠️
pymongo/synchronous/client_session.py	83.33%	0 Missing and 1 partial ⚠️

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