PYTHON-5745 Consolidate command telemetry

[blink1073]

PYTHON-5745

Changes in this PR

Introduces pymongo/_telemetry.py with a _CommandTelemetry class that unifies structured logging and APM event publishing for command lifecycle events into a single internal API. This refactor is a stepping stone to adding OpenTelemetry support in a _telemetry.py, so all event-related handling is in one centralized location.

Test Plan

No new tests: this is a behavior-preserving refactor. The existing APM / command-monitoring and command-logging spec suites assert the exact event and log documents that any regression would change.

Checklist

Checklist for Author

• Did you update the changelog (if necessary)? — Not necessary; internal refactor with no user-facing behavior change.
• Is there test coverage? — Covered by existing spec suites (behavior preserved).
• Is any followup work tracked in a JIRA ticket? If so, add link(s). — PYTHON-5846 will extend this pattern to cover the remaining logging and APM event types.

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

✅ All modified and coverable lines are covered by tests.

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