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/cohere/cohere_provider.py

@@ -0,0 +1,24 @@
+"""Cohere embeddings provider."""
+
+from chromadb.utils.embedding_functions.cohere_embedding_function import (
+    CohereEmbeddingFunction,
+)
+from pydantic import Field
+
+from crewai.rag.core.base_embeddings_provider import BaseEmbeddingsProvider
+
+
+class CohereProvider(BaseEmbeddingsProvider[CohereEmbeddingFunction]):
+    """Cohere embeddings provider."""
+
+    embedding_callable: type[CohereEmbeddingFunction] = Field(
+        default=CohereEmbeddingFunction, description="Cohere embedding function class"
+    )
+    api_key: str = Field(
+        description="Cohere API key", validation_alias="COHERE_API_KEY"
+    )
+    model_name: str = Field(
+        default="large",
+        description="Model name to use for embeddings",
+        validation_alias="COHERE_MODEL_NAME",
+    )