feat(llmobs): add Anthropic LLMObs Integration

[wconti27]

This PR adds LLM Observability for Anthropic messages.

Checklist

• Change(s) are motivated and described in the PR description
• Testing strategy is described if automated tests are not included in the PR
• Risks are described (performance impact, potential for breakage, maintainability)
• Change is maintainable (easy to change, telemetry, documentation)
• Library release note guidelines are followed or label changelog/no-changelog is set
• Documentation is included (in-code, generated user docs, public corp docs)
• Backport labels are set (if applicable)
• If this PR changes the public interface, I've notified @DataDog/apm-tees.

Reviewer Checklist

• Title is accurate
• All changes are related to the pull request's stated goal
• Description motivates each change
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Change is maintainable (easy to change, telemetry, documentation)
• Release note makes sense to a user of the library
• 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

[datadog-dd-trace-py-rkomorn]

Datadog Report

Branch report: conti/add-anthropic-mlobs-methods
Commit report: 51f3fc6
Test service: dd-trace-py

✅ 0 Failed, 176975 Passed, 1900 Skipped, 11h 45m 7.67s Total duration (34m 8.47s time saved)
❄️ 6 New Flaky
⌛ 1 Performance Regression

New Flaky Tests (6)

• test_chain_invoke_str_input - test_langchain_community.py - Last Failure

  Expand for error

   At request <Request GET /test/session/snapshot >:
      At snapshot (token='tests.contrib.langchain.test_langchain_community.test_chain_invoke'):
       - Directory: /snapshots
       - CI mode: 1
       - Trace File: /snapshots/tests.contrib.langchain.test_langchain_community.test_chain_invoke.json
       - Stats File: /snapshots/tests.contrib.langchain.test_langchain_community.test_chain_invoke_tracestats.json
       At compare of 1 expected trace(s) to 1 received trace(s):
        At trace 'langchain.request' (2 spans):
         At snapshot compare of span 'langchain.request' at position 1 in trace:
          - Expected span:
   ...
  

• test_lcel_chain_simple - test_langchain_community.py - Last Failure

  Expand for error

   At request <Request GET /test/session/snapshot >:
      At snapshot (token='tests.contrib.langchain.test_langchain_community.test_lcel_chain_simple'):
       - Directory: /snapshots
       - CI mode: 1
       - Trace File: /snapshots/tests.contrib.langchain.test_langchain_community.test_lcel_chain_simple.json
       - Stats File: /snapshots/tests.contrib.langchain.test_langchain_community.test_lcel_chain_simple_tracestats.json
       At compare of 1 expected trace(s) to 1 received trace(s):
        At trace 'langchain.request' (2 spans):
         At snapshot compare of span 'langchain.request' at position 1 in trace:
          - Expected span:
   ...
  

• test_openai_chat_model_sync_generate - test_langchain_community.py - Last Failure

  Expand for error

   At request <Request GET /test/session/snapshot >:
      At snapshot (token='tests.contrib.langchain.test_langchain_community.test_openai_chat_model_sync_generate'):
       - Directory: /snapshots
       - CI mode: 1
       - Trace File: /snapshots/tests.contrib.langchain.test_langchain_community.test_openai_chat_model_sync_generate.json
       - Stats File: /snapshots/tests.contrib.langchain.test_langchain_community.test_openai_chat_model_sync_generate_tracestats.json
       At compare of 1 expected trace(s) to 1 received trace(s):
        At trace 'langchain.request' (1 spans):
         At snapshot compare of span 'langchain.request' at position 1 in trace:
          - Expected span:
   ...
  

• test_llmobs_anthropic_chat_model - test_langchain_llmobs.py - Last Failure

  Expand for error

   Attempted to access streaming response content, without having called \`read()\`.
  

• test_llmobs_chain_schema_io - test_langchain_llmobs.py - Last Failure

  Expand for error

   Attempted to access streaming response content, without having called \`read()\`.
  

⌛ Performance Regressions vs Default Branch (1)

• test_export_reset - test_http.py 6.41s (+5.35s, +504%) - Details

[erikayasuda]

@wconti27 LGTM just needs a release note 👍