When calling non-text-embedding-3 models routed through the openai provider
(e.g. nvidia/llama-3.2-nv-embedqa-1b-v2), passing `dimensions` previously
raised an UnsupportedParamsError unconditionally. This fix threads
`allowed_openai_params` through the embedding call stack so that providers
can opt-in to passing `dimensions` by including it in the list.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>