feat(llmobs): add pydantic_ai instrumentation

[Kyle-Verhoog]

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/contrib/internal/pydantic_ai/patch.py                           @DataDog/ml-observability
tests/llmobs/pydantic_ai/__init__.py                                    @DataDog/ml-observability
tests/llmobs/pydantic_ai/test_pydantic_ai.py                            @DataDog/ml-observability
.github/CODEOWNERS                                                      @DataDog/python-guild @DataDog/apm-core-python
ddtrace/_monkey.py                                                      @DataDog/apm-core-python
ddtrace/llmobs/_llmobs.py                                               @DataDog/ml-observability
ddtrace/settings/_config.py                                             @DataDog/apm-core-python
riotfile.py                                                             @DataDog/apm-python
tests/contrib/openai/test_openai_v1.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: 276 ± 3 ms.

The average import time from base is: 277 ± 3 ms.

The import time difference between this PR and base is: -1.7 ± 0.1 ms.

Import time breakdown

The following import paths have shrunk:

ddtrace.auto 1.923 ms (0.70%)

ddtrace.bootstrap.sitecustomize 1.247 ms (0.45%)

ddtrace.bootstrap.preload 1.247 ms (0.45%)

ddtrace.internal.remoteconfig.client 0.632 ms (0.23%)

ddtrace 0.676 ms (0.25%)

ddtrace.internal._unpatched 0.026 ms (0.01%)