PYTHON-6045 Add error.type OpenTelemetry command span attribute

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PYTHON-6045

Fifth in the OpenTelemetry stack, on top of the four PRs splitting #2964. Base is PYTHON-5947-otel-4-getmore.

	Branch	Contents
1	PYTHON-5947-otel-1-operations	operation spans
2	PYTHON-5947-otel-2-transactions	transaction spans
3	PYTHON-5947-otel-3-unified	unified runner and vendored fixtures
4	PYTHON-5947-otel-4-getmore	getMore spans
5	PYTHON-5947-otel-5-error-type	error.type command span attribute (this PR)

Implements the error.type command span attribute specified by DRIVERS-3617 (mongodb/specifications#1974). error.type is the span-level dimension OpenTelemetry backends group and alert on; carried only as the exception event's exception.type, error class cannot be aggregated on.

Changes in this PR

• end_command_span_failure sets error.type on command spans: the server error code when one is present (mirroring db.response.status_code), otherwise the exception's qualified class name.
• _set_exception_attributes returns the computed exception.type so the fallback reuses it.
• Operation spans deliberately omit error.type, per the spec: an operation can succeed via retry even when an underlying command failed.
• Synced the new error_type.json spec fixture.

Test Plan

• Spec fixture test/open_telemetry/operation/error_type.json: server error (error.type matches db.response.status_code) and closed connection (db.response.status_code absent, error.type is the class name). Both assert the operation span has no error.type.
• Unit tests for the class-name fallback: ConnectionFailure and NetworkTimeout. Verified both fail if the fallback branch is removed.
• Extended the existing server-error test to assert error.type mirrors db.response.status_code.
• Full otel suite: 103 passed, 1 skipped (unrelated mapReduce deprecation). just lint and just typing clean.
• Evergreen otel-rhel8: #10898 — success, 0 failed tasks.

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?

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Superseded by #3000, which has its head branch on this repo rather than my fork so it can join the stack in GitHub's UI (fork PRs cannot be stacked). Same commits, same base.