Span ID reported when "X-Cloud-Trace-Context" is used is incorrect

[michaelsafyan]

For Googlers: motivating details / context can be found in Buganizer issue # 367762417

Steps to reproduce

1. Execute in an environment in which tracing context has been supplied via X-Cloud-Trace-Context.

Observed

The LogEntry that is created contains a span_id that is incorrect.

Note that LogEntry.span_id should be the hexadecimal encoding of the span ID, whereas X-Cloud-Trace-Context (unlike traceparent) encodes the span_id in decimal format.

Expected

The LogEntry.span_id field should be populated with the canonical (hexadecimal) representation of the span ID.

[michaelsafyan]

Additional context:

It looks like the helper file located here:

• https://github.com/googleapis/python-logging/blob/main/google/cloud/logging_v2/handlers/_helpers.py

May need to update _parse_xcloud_trace to convert the span ID to hex