fix(distributed_tracing): ensure ASM standalone operates on all propagation styles

[mabdinur]

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-asm-standalone-propagation-7bdb5a040ef82bac.yaml  @DataDog/apm-python
ddtrace/propagation/http.py                                             @DataDog/apm-sdk-api-python

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: munir/maybe-fix-asm-standalone-propagation
Commit report: 5126ddc
Test service: dd-trace-py

✅ 0 Failed, 1152 Passed, 316 Skipped, 21m 37.1s Total duration (15m 48.29s time saved)

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-01-08 17:53:39

Comparing candidate commit 5126ddc in PR branch munir/maybe-fix-asm-standalone-propagation with baseline commit 3d08709 in branch main.

Found 0 performance improvements and 4 performance regressions! Performance is the same for 390 metrics, 2 unstable metrics.

scenario:iast_aspects-ospathjoin_aspect

• 🟥 execution_time [+372.694ns; +443.923ns] or [+7.261%; +8.648%]

scenario:iast_aspects-ospathsplit_aspect

• 🟥 execution_time [+369.232ns; +436.139ns] or [+9.676%; +11.429%]

scenario:iast_aspects-ospathsplitdrive_aspect

• 🟥 execution_time [+199.907ns; +238.812ns] or [+7.552%; +9.021%]

scenario:iast_aspects-replace_aspect

• 🟥 execution_time [+606.813ns; +689.944ns] or [+8.936%; +10.161%]

[Yun-Kim]

Moving the ASM distributed header propagation to HTTPPropagator makes sense, but just a little confused why this behavior (disregarded whether tracer was enabled or not) was occuring in the first place.

[Yun-Kim]

Just to clarify - previously we were only propagating ASM distributed tracing headers on Datadog headers regardless if tracing was enabled/disabled? Is this because DatadogMultiHeaders._inject() doesn't account for tracing being enabled/disabled?