improve Otel tracing (#6499)

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## Why are these changes needed?

Will the changes made in
https://github.com/microsoft/autogen/pull/5853/files and this PR need to
be ported to the worker_runtime as well?
Resolves https://github.com/microsoft/autogen/issues/5894

## Related issue number

https://github.com/microsoft/autogen/issues/5894

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