PYTHON-6027 Consolidate non-IO code in Topology into shared base class

[sleepyStick]

PYTHON-6027

Changes in this PR

Test Plan

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?

[Copilot]

🟡 Changes recommended

Existing test helpers still access the removed name-mangled events executor attribute.

1 open finding

• Update tests for renamed _events_executor attribute · New

What changed in this PR

Consolidates duplicated synchronous/asynchronous topology logic into a shared base class.

Changes:

• Adds generic pool typing.
• Extracts common topology state and methods.
• Retains I/O-specific behavior in concrete topology classes.

File	Description
pymongo/​typings.py	Adds shared pool typing.
pymongo/​topology_shared.py	Introduces the shared topology base.
pymongo/​synchronous/​topology.py	Uses the shared base.
pymongo/​asynchronous/​topology.py	Uses the shared base.

🧠 Review effort: Balanced

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[codecov]

Codecov Report

❌ Patch coverage is 92.90323% with 11 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pymongo/topology_shared.py	91.53%	10 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!

[Copilot]

🟢 Approval recommended

The refactor preserves behavior across both topology variants, and construction through the shared base succeeds.

1 open finding

• Update tests for renamed _events_executor attribute

🧠 Review effort: Balanced

[Copilot]

🟢 Approval recommended

The refactor preserves existing behavior and all affected internal attribute references were updated consistently.

0 open findings

1 resolved since last review

• Update tests for renamed _events_executor attribute

🧠 Review effort: Balanced

[codeowners-service-app]

Assigned caseyclements for team dbx-python because aclark4life is out of office.

[aclark4life]

Now a private method so maybe:
"Shared base for the sync and async classes."

[sleepyStick]

i assume this comment is for _AgnosticTopologyBase? and if so, fixed in 47d6c9c (it didnt make sense for _ErrorContext imo)

[aclark4life]

LGTM