sentence-transformers safetensors mpnet sentence-similarity feature-extraction dataset_size:n<1K loss:MultipleNegativesRankingLoss arxiv:1908.10084 arxiv:1705.00652 base_model:sentence-transformers/all-mpnet-base-v2 base_model:finetune:sentence-transformers/all-mpnet-base-v2 autotrain_compatible endpoints_compatible region:us