huggingface_hub: Instrument feature_extraction (embeddings)

[ericapisani]

InferenceClient.feature_extraction() is the HuggingFace equivalent of embeddings. The SDK has OP.GEN_AI_EMBEDDINGS defined and both OpenAI and Cohere instrument their embedding methods. This is a meaningful gap for users who use HF for embeddings. Should cover both sync InferenceClient and async AsyncInferenceClient.

[linear-code]

PY-2253