fix(celery): account for a chains scenario

We've made a few changes to handle celery context recently:

In particular the goal of https://github.com/DataDog/dd-trace-py/pull/10676 was to handle a scenario where a long running task may run into an exception, preventing it from closing.

Unfortunately, this scenario did not account for cases where tasks are chained and may not close until later.

See: https://github.com/DataDog/dd-trace-py/issues/11479

With this PR, the sample app in https://github.com/DataDog/dd-trace-py/issues/11479 would attach the celery specific span back to the root span.

This is a draft PR for now because I am waiting to see if there are unexpected failures if we remove the logic to close unclosed prerun spans in some cases. (Some more testing on this is needed).

I also need to add tests for the chains scenario.

Checklist

[ ] PR author has checked that all the criteria below are met
The PR description includes an overview of the change
The PR description articulates the motivation for the change
The change includes tests OR the PR description describes a testing strategy
The PR description notes risks associated with the change, if any
Newly-added code is easy to change
The change follows the library release note guidelines
The change includes or references documentation updates if necessary
Backport labels are set (if applicable)

Reviewer Checklist

[ ] Reviewer has checked that all the criteria below are met
Title is accurate
All changes are related to the pull request's stated goal
Avoids breaking API changes
Testing strategy adequately addresses listed risks
Newly-added code is easy to change
Release note makes sense to a user of the library
If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
Backport labels are set in a manner that is consistent with the release branch maintenance policy

DataDog / dd-trace-py

fix(celery): account for a chains scenario #11498

Checklist

Reviewer Checklist