chore(profiler): span link independent from context provider

[P403n1x87]

We make sure that the span link mechanism in the profiler is independent from the context provider, as this can change with calls to configure. Instead we rely on the core event hub to emit an event when a span is activated so that the profiler can perform the linking with the corresponding thread.

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:

ddtrace/_trace/tracer.py                                                @DataDog/apm-sdk-api-python
ddtrace/internal/datadog/profiling/stack_v2/__init__.py                 @DataDog/profiling-python
ddtrace/profiling/collector/stack.pyx                                   @DataDog/profiling-python

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: chore/profiler-span-link
Commit report: 8bc9610
Test service: dd-trace-py

✅ 0 Failed, 964 Passed, 322 Skipped, 21m 27.87s Total duration (16m 40.09s time saved)

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-12-19 12:16:11

Comparing candidate commit bd4be9a in PR branch chore/profiler-span-link with baseline commit 2813291 in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 362 metrics, 2 unstable metrics.

[P403n1x87]

Related #12135

[P403n1x87]

We can revisit if and when needed.