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 error.type on command spans, specified by DRIVERS-3617 (mongodb/specifications#1974). OpenTelemetry backends group and alert on span attributes, so an error class carried only by the exception event cannot be queried at the span level.

Changes in this PR

• end_command_span_failure sets error.type to the server error code when the reply carries one, otherwise to the exception's qualified class name.
• _set_exception_attributes returns the computed exception.type so the fallback reuses it.
• Operation spans omit error.type, because an operation can succeed through a retry even when a command failed.
• Synced the new error_type.json spec fixture.

Test Plan

• Spec fixture error_type.json covers a server error, where error.type matches db.response.status_code, and a closed connection, where it falls back to the class name.
• New unit tests cover the fallback for ConnectionFailure and NetworkTimeout. 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 passes. just lint and just typing are clean.
• Evergreen otel-rhel8 patch #10898 passed with 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?