PYTHON-6021 Move _write_concern_for_cmd into BaseObject

[sleepyStick]

PYTHON-6021

Changes in this PR

Move _write_concern_for_cmd into BaseObject

Test Plan

existing tests should continue to pass :)

Checklist

Checklist for Author

• [NA] Did you update the changelog (if necessary)?
• Is there test coverage?
• [NA] 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]

Codecov Report

❌ Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pymongo/common.py	60.00%	1 Missing and 1 partial ⚠️

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