[java-datastore] For transaction operations, OpenTelemetry Trace spans not exhibiting correct hierarchy - all operations must be nested under the Run method.


![nested span issue for transactions](https://github.com/googleapis/google-cloud-java/assets/57637300/d1b3b8ba-4387-4130-b197-a06ff3a715a5)
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