Support for OpenAI-compatible embedding endpoints

[titusz]

Several self-hosted embedding servers expose OpenAI-compatible /embeddings endpoints:

• Infinity
• vLLM
• Ollama

The current OpenAI provider has a hardcoded API_BASE_URL. A configurable base_url
would make all these work without needing separate provider implementations.

Possible API

client = Client()
response = client.embed(
    model="BAAI/bge-small-en-v1.5",
    inputs=["Hello world"],
    base_url="http://localhost:7997"  # or via env var
)

Since the request format is already OpenAI-compatible, only the URL routing would change.

Thanks for catsu, the unified API and model metadata catalog are really useful!