feat: add HuggingFace Hub integration

[Abhijeet Prasad (AbhiPrasad)]

resolves #278

Adds native Braintrust tracing for the Hugging Face Hub Python SDK (huggingface_hub) via the integrations API. The integration supports huggingface-hub>=0.32.0 and is included in auto_instrument() by default.

How to enable it:

import braintrust
from braintrust import init_logger
from huggingface_hub import InferenceClient

logger = init_logger(project="my-project")
braintrust.auto_instrument()  # enables huggingface_hub unless disabled

client = InferenceClient(provider="auto")
with logger.start_span(name="hf request"):
    response = client.chat_completion(
        model="meta-llama/Llama-3.1-8B-Instruct",
        messages=[{"role": "user", "content": "Say hello"}],
        max_tokens=32,
    )

The integration can also be enabled explicitly or disabled from the global auto-instrumentation call:

from braintrust.auto import auto_instrument

auto_instrument(huggingface_hub=True)
auto_instrument(huggingface_hub=False)  # opt out

For manual wrapping, wrap individual sync or async clients:

from braintrust.integrations.huggingface_hub import wrap_huggingface_hub
from huggingface_hub import AsyncInferenceClient, InferenceClient

client = wrap_huggingface_hub(InferenceClient(provider="auto"))
async_client = wrap_huggingface_hub(AsyncInferenceClient(provider="auto"))

Features added:

• Traces sync and async InferenceClient calls for chat_completion, text_generation, feature_extraction, and sentence_similarity.
• Covers the OpenAI-compatible chat alias client.chat.completions.create(...) because it proxies through chat_completion.
• Supports non-streaming and streaming chat completions, including async streams, context manager finalization, early stream close handling, and nesting under parent Braintrust spans.
• Captures span inputs, outputs, allowlisted request metadata, provider/model routing metadata, response identifiers, finish reasons, and token metrics from Hugging Face response usage/details fields.
• Logs provider errors to the span before re-raising.
• Adds VCR-backed coverage for latest and 0.32.0 Hugging Face Hub SDKs, plus an auto-instrumentation smoke test.
• Adds the test_huggingface_hub nox session, dependency matrix entries, and cassette-directory mapping for provider-versioned cassette hygiene.