fix: kafka consumer parenting logic

[wconti27]

Fixes bug where Kafka consumer was creating unparented spans when consuming a message with no context present.

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-kafka-consumer-parenting-29acfd08e05d2350.yaml   @DataDog/apm-python
ddtrace/contrib/internal/kafka/patch.py                                 @DataDog/apm-core-python @DataDog/apm-idm-python
tests/contrib/kafka/test_kafka.py                                       @DataDog/apm-core-python @DataDog/apm-idm-python

[pr-commenter]

Benchmarks

Benchmark execution time: 2024-12-11 15:58:39

Comparing candidate commit 8a0d205 in PR branch conti/fix-kafka-consumer-parenting with baseline commit 2e2303b in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 394 metrics, 2 unstable metrics.

[emmettbutler]

This could use a regression test and a release note

[wconti27]

/merge

[dd-devflow]

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2024-12-11 17:12:59 UTC ℹ️ MergeQueue: pull request added to the queue

The median merge time in main is 31m.

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