chore(llmobs): only register llmobs hooks when llm obs enabled

[lievan]

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/llmobs/_llmobs.py                                               @DataDog/ml-observability
tests/llmobs/test_llmobs_ragas_faithfulness_evaluator.py                @DataDog/ml-observability

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: evan.li/fix-dual-writes
Commit report: 28e8830
Test service: dd-trace-py

✅ 0 Failed, 87 Passed, 1468 Skipped, 4m 10.82s Total duration (35m 37.85s time saved)

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-01-09 22:27:23

Comparing candidate commit 28e8830 in PR branch evan.li/fix-dual-writes with baseline commit 04ee68f in branch main.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 380 metrics, 2 unstable metrics.