feat: add custom embedding types and migrate providers

- introduce baseembeddingsprovider and helper for embedding functions  
- add core embedding types and migrate providers, factory, and storage modules  
- remove unused type aliases and fix pydantic schema error  
- update providers with env var support and related fixes

src/crewai/rag/embeddings/providers/text2vec/text2vec_provider.py

@@ -0,0 +1,22 @@
+"""Text2Vec embeddings provider."""
+
+from chromadb.utils.embedding_functions.text2vec_embedding_function import (
+    Text2VecEmbeddingFunction,
+)
+from pydantic import Field
+
+from crewai.rag.core.base_embeddings_provider import BaseEmbeddingsProvider
+
+
+class Text2VecProvider(BaseEmbeddingsProvider[Text2VecEmbeddingFunction]):
+    """Text2Vec embeddings provider."""
+
+    embedding_callable: type[Text2VecEmbeddingFunction] = Field(
+        default=Text2VecEmbeddingFunction,
+        description="Text2Vec embedding function class",
+    )
+    model_name: str = Field(
+        default="shibing624/text2vec-base-chinese",
+        description="Model name to use",
+        validation_alias="TEXT2VEC_MODEL_NAME",
+    )