fix(llmobs): make sure correct llmobs trace id is returned from export_span [backport 3.9]

[github-actions]

Backport f5bed1c from #13620 to 3.9.

We recently changed how we record our LLMObs trace IDs - from APM trace IDs to new randomly generated ones. However, we missed updating export_span. This PR ensures we export the correct trace ID from export_span.

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/llmobs-fix-incorrect-exported-trace-id-d35aeea97a8419c4.yaml  @DataDog/apm-python
ddtrace/llmobs/_llmobs.py                                               @DataDog/ml-observability
tests/llmobs/test_llmobs_service.py                                     @DataDog/ml-observability

[github-actions]

Bootstrap import analysis

Comparison of import times between this PR and base.

Summary

The average import time from this PR is: 282 ± 4 ms.

The average import time from base is: 285 ± 4 ms.

The import time difference between this PR and base is: -3.1 ± 0.2 ms.

Import time breakdown

The following import paths have shrunk:

ddtrace.auto 2.064 ms (0.73%)

ddtrace.bootstrap.sitecustomize 1.384 ms (0.49%)

ddtrace.bootstrap.preload 1.384 ms (0.49%)

ddtrace.internal.remoteconfig.client 0.670 ms (0.24%)

ddtrace 0.681 ms (0.24%)

ddtrace.internal._unpatched 0.024 ms (0.01%)

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-06-06 21:49:55

Comparing candidate commit 0735889 in PR branch backport-13620-to-3.9 with baseline commit eff5773 in branch 3.9.

Found 0 performance improvements and 4 performance regressions! Performance is the same for 549 metrics, 3 unstable metrics.

scenario:iastaspects-format_map_aspect

• 🟥 execution_time [+295.438ns; +414.568ns] or [+9.092%; +12.759%]

scenario:iastaspects-upper_aspect

• 🟥 execution_time [+200.165ns; +233.588ns] or [+8.812%; +10.283%]

scenario:iastaspectsospath-ospathjoin_aspect

• 🟥 execution_time [+887.862ns; +968.985ns] or [+14.458%; +15.779%]

scenario:telemetryaddmetric-flush-1-metric

• 🟥 execution_time [+320.141ns; +488.793ns] or [+7.627%; +11.645%]