HPCC-31425 Add support for tracking the active span in the thread context

[ghalliday]

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[github-actions]

https://track.hpccsystems.com/browse/HPCC-31425
Jira updated

[ghalliday]

@rpastrana this is the next logical step for managing the spans.

This is a draft because it it pushed to check it runs, and also there are still some potential issues.

At the moment I have combined the functionality into OwnedSpanScope, but there may be problems with that - it implies the spanscope will be destroyed on the same thread that it was set. That needs more thought. Possibly splitting the class in two, or having one derived from the other.

There should also be comments about why ISpan is not linked in the saved context (and there should be a discussion).

Assuming this is merged in some form, your code to report the span ids in the logging should become trivial - by linking the span object, and then accessing fields from it to log.

[rpastrana]

this seems fine, but I wish there was a version of clear that doesn't setThreadedActiveSpan(prevSpan); since we're about the call setThreadedActiveSpan(_span)

[rpastrana]

@ghalliday seems fine. I didn't see the comments you wanted to add regarding not linked span

[ghalliday]

@ghalliday seems fine. I didn't see the comments you wanted to add regarding not linked span

Now added.