fix: correct the parent class of CacheEmbedding (#2578)

api/core/embedding/cached_embedding.py

 from typing import Optional, cast
 
 import numpy as np
-from langchain.embeddings.base import Embeddings
 from sqlalchemy.exc import IntegrityError
 
 from core.model_manager import ModelInstance
 from core.model_runtime.entities.model_entities import ModelPropertyKey
 from core.model_runtime.model_providers.__base.text_embedding_model import TextEmbeddingModel
+from core.rag.datasource.entity.embedding import Embeddings
 from extensions.ext_database import db
 from extensions.ext_redis import redis_client
 from libs import helper