feat(anthropic): add Messages.create sync instrumentation

[vasantteja]

Description

Implements OpenTelemetry instrumentation for Anthropic's Messages.create API (sync, non-streaming). This adds automatic tracing for Anthropic SDK calls, capturing GenAI semantic convention attributes for observability.

P.S: LLM help was used for writing the code.

What's Implemented

• patch.py: Wrapper function for Messages.create that creates spans with request/response attributes
• utils.py: Helper functions for attribute extraction, error handling, and content capture configuration
• __init__.py: Wiring for patching/unpatching via wrapt
• Tests: Comprehensive test suite with VCR cassettes for API mocking
• Updated minimum anthropic version to 0.16.0 - the instrumentation requires the modern SDK structure (anthropic.resources.messages module) which doesn't exist in versions prior to 0.18.0.

Semantic Convention Attributes Captured

Request:

• gen_ai.operation.name (chat)
• gen_ai.system (anthropic)
• gen_ai.request.model
• gen_ai.request.max_tokens
• gen_ai.request.temperature
• gen_ai.request.top_p
• gen_ai.request.top_k
• gen_ai.request.stop_sequences
• server.address

Response:

• gen_ai.response.id
• gen_ai.response.model
• gen_ai.response.finish_reasons
• gen_ai.usage.input_tokens
• gen_ai.usage.output_tokens

Error:

• error.type (on exceptions)

Fixes #(https://github.com/open-telemetry/opentelemetry-python-contrib/issues/3949)

Type of change

• [x] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

Ran the full test suite with VCR cassettes for mocked API responses:

pytest instrumentation-genai/opentelemetry-instrumentation-anthropic/tests/ -v

Test cases:

• [x] Basic sync message creation with correct span attributes
• [x] All optional parameters (temperature, top_p, top_k, stop_sequences)
• [x] Token usage capture (input/output tokens)
• [x] Stop reason captured as finish_reasons array
• [x] Connection error handling (APIConnectionError)
• [x] API error handling (404 NotFoundError)
• [x] Uninstrumentation removes patching
• [x] Multiple instrument/uninstrument cycles

Results: 15 tests passed (8 new + 7 existing instrumentor tests)

Does This PR Require a Core Repo Change?

• [x] No.

Checklist:

• [x] Followed the style guidelines of this project
• [x] Changelogs have been updated
• [x] Unit tests have been added
• [x] Documentation has been updated