fix: fix type hints on DocumentStore protocol (#6383)

* fix type hints

* disable specific pylint checker

haystack/preview/document_stores/protocols.py

@@ -5,6 +5,9 @@
 from haystack.preview.dataclasses import Document
 
 
+# Ellipsis are needed for the type checker, it's safe to disable module-wide
+# pylint: disable=unnecessary-ellipsis
+
 logger = logging.getLogger(__name__)
 
 
@@ -29,17 +32,20 @@ def to_dict(self) -> Dict[str, Any]:
         """
         Serializes this store to a dictionary.
         """
+        ...
 
     @classmethod
     def from_dict(cls, data: Dict[str, Any]) -> "DocumentStore":
         """
         Deserializes the store from a dictionary.
         """
+        ...
 
     def count_documents(self) -> int:
         """
         Returns the number of documents stored.
         """
+        ...
 
     def filter_documents(self, filters: Optional[Dict[str, Any]] = None) -> List[Document]:
         """
@@ -112,6 +118,7 @@ def filter_documents(self, filters: Optional[Dict[str, Any]] = None) -> List[Doc
         :param filters: the filters to apply to the document list.
         :return: a list of Documents that match the given filters.
         """
+        ...
 
     def write_documents(self, documents: List[Document], policy: DuplicatePolicy = DuplicatePolicy.FAIL) -> int:
         """
@@ -128,6 +135,7 @@ def write_documents(self, documents: List[Document], policy: DuplicatePolicy = D
             If DuplicatePolicy.OVERWRITE is used, this number is always equal to the number of documents in input.
             If DuplicatePolicy.SKIP is used, this number can be lower than the number of documents in the input list.
         """
+        ...
 
     def delete_documents(self, document_ids: List[str]) -> None:
         """
@@ -136,3 +144,4 @@ def delete_documents(self, document_ids: List[str]) -> None:
 
         :param object_ids: the object_ids to delete
         """
+        ...