fix(futures): ensure child spans are correctly parented in Threadpools

[mabdinur]

Introduces a private API for activating a trace Context in a contextmanager.

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

[github-actions]

CODEOWNERS have been resolved as:

releasenotes/notes/fix-futures-parenting-3a53b94ee05dff93.yaml          @DataDog/apm-python
ddtrace/_trace/context.py                                               @DataDog/apm-sdk-api-python
ddtrace/_trace/provider.py                                              @DataDog/apm-sdk-api-python
ddtrace/_trace/span.py                                                  @DataDog/apm-sdk-api-python
ddtrace/_trace/tracer.py                                                @DataDog/apm-sdk-api-python
ddtrace/contrib/internal/futures/threading.py                           @DataDog/apm-core-python @DataDog/apm-idm-python
tests/contrib/futures/test_propagation.py                               @DataDog/apm-core-python @DataDog/apm-idm-python
tests/tracer/test_tracer.py                                             @DataDog/apm-sdk-api-python

[github-actions]

Bootstrap import analysis

Comparison of import times between this PR and base.

Summary

The average import time from this PR is: 231 ± 2 ms.

The average import time from base is: 233 ± 3 ms.

The import time difference between this PR and base is: -1.9 ± 0.1 ms.

Import time breakdown

The following import paths have grown:

ddtrace.auto 0.040 ms (0.02%)

ddtrace 0.040 ms (0.02%)

ddtrace.trace 0.040 ms (0.02%)

ddtrace._trace.tracer 0.040 ms (0.02%)

The following import paths have shrunk:

ddtrace.auto 1.991 ms (0.86%)

ddtrace.bootstrap.sitecustomize 1.267 ms (0.55%)

ddtrace.bootstrap.preload 1.267 ms (0.55%)

ddtrace.internal.products 1.267 ms (0.55%)

ddtrace.internal.remoteconfig.client 0.620 ms (0.27%)

ddtrace 0.724 ms (0.31%)

ddtrace.trace 0.056 ms (0.02%)

ddtrace._trace.provider 0.056 ms (0.02%)

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-05-02 17:18:26

Comparing candidate commit cd1a331 in PR branch munir/fix-futures-integration with baseline commit 8fe0cfa in branch main.

Found 1 performance improvements and 1 performance regressions! Performance is the same for 512 metrics, 6 unstable metrics.

scenario:iastdjangostartup-iast

• 🟩 execution_time [-461.910ms; -241.854ms] or [-19.360%; -10.137%]

scenario:otelspan-start

• 🟥 execution_time [+3.011ms; +5.132ms] or [+7.208%; +12.288%]

[github-actions]

The backport to 2.21 failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-2.21 2.21
# Navigate to the new working tree
cd .worktrees/backport-2.21
# Create a new branch
git switch --create backport-13168-to-2.21
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 40fe58d21ae0abde036e9fc36bd0420f4efe7d6e
# Push it to GitHub
git push --set-upstream origin backport-13168-to-2.21
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-2.21

Then, create a pull request where the base branch is 2.21 and the compare/head branch is backport-13168-to-2.21.