Implements embed() on FeatherlessClient. Featherless's OpenAI-
compatible surface does NOT expose /v1/embeddings at the time of
writing, so this implementation raises NotImplementedError rather
than issuing a request that would 404. The
chat.services.embeddings.generate_embedding wrapper (T112.3)
catches the exception and degrades to the zero-vector fallback path
(plus the existing T107 warning) — misconfigured callers fail loudly
in logs while the request path keeps working.
If/when Featherless ships embeddings, swap the body for
self._client.embeddings.create(model=..., input=...) guarded by
the existing 2-conn semaphore (mirrors generate/stream). The Protocol
seam in T112.1 is already wired so no other code needs to change.
Adds tests/test_featherless.py pinning the NotImplementedError
contract.
Joseph Doherty