HuggingFaceEndpointEmbeddings missing bill_to / additional_headers parameter

### Submission checklist - [x] This is a bug, not a usage question. - [x] I added a clear and descriptive title that summarizes this issue. - [x] I used the GitHub search to find a similar question and didn't find it. - [x] I am sure that this is a bug in LangChain rather than my code. - [x] The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package). - [x] This is not related to the langchain-community package. - [x] I posted a self-contained, minimal, reproducible example. A maintainer can copy it and run it AS IS. ### Package (Required) - [ ] langchain - [ ] langchain-openai - [ ] langchain-anthropic - [ ] langchain-classic - [ ] langchain-core - [ ] langchain-model-profiles - [ ] langchain-tests - [ ] langchain-text-splitters - [ ] langchain-chroma - [ ] langchain-deepseek - [ ] langchain-exa - [ ] langchain-fireworks - [ ] langchain-groq - [x] langchain-huggingface - [ ] langchain-mistralai - [ ] langchain-nomic - [ ] langchain-ollama - [ ] langchain-openrouter - [ ] langchain-perplexity - [ ] langchain-qdrant - [ ] langchain-xai - [ ] Other / not sure / general ### Related Issues / PRs _No response_ ### Reproduction Steps / Example Code (Python) ```python from langchain_huggingface import HuggingFaceEndpointEmbeddings model = "sentence-transformers/all-mpnet-base-v2" hf = HuggingFaceEndpointEmbeddings( model=model, task="feature-extraction", huggingfacehub_api_token="my-api-key", # Fine grained token with "Make calls to Inference Providers on behalf of the selected organizations" ) hf.embed_query("This is a test query") ``` ### Error Message and Stack Trace (if applicable) ```shell huggingface_hub.errors.HfHubHTTPError: Client error '401 Unauthorized' for url 'https://router.huggingface.co/hf-inference/models/sentence-transformers/all-mpnet-base-v2/pipeline/feature-extraction' ``` ### Description The deprecated `HuggingFaceInferenceAPIEmbeddings` (from `langchain_community`) accepts an `additi…