core: Add ruff rules D (docstring) (#29406)

This ensures that the code is properly documented:
https://docs.astral.sh/ruff/rules/#pydocstyle-d

Related to #21983

libs/core/langchain_core/documents/__init__.py

@@ -1,4 +1,6 @@
-"""**Document** module is a collection of classes that handle documents
+"""Documents module.
+
+**Document** module is a collection of classes that handle documents
 and their transformations.
 
 """

libs/core/langchain_core/documents/base.py

@@ -1,3 +1,5 @@
+"""Base classes for media and documents."""
+
 from __future__ import annotations
 
 import contextlib
@@ -45,6 +47,11 @@ class BaseMedia(Serializable):
 
     @field_validator("id", mode="before")
     def cast_id_to_str(cls, id_value: Any) -> Optional[str]:
+        """Coerce the id field to a string.
+
+        Args:
+            id_value: The id value to coerce.
+        """
         if id_value is not None:
             return str(id_value)
         else:
@@ -291,7 +298,10 @@ class Document(BaseMedia):
 
     @classmethod
     def get_lc_namespace(cls) -> list[str]:
-        """Get the namespace of the langchain object."""
+        """Get the namespace of the langchain object.
+
+        Default namespace is ["langchain", "schema", "document"].
+        """
         return ["langchain", "schema", "document"]
 
     def __str__(self) -> str:

libs/core/langchain_core/documents/compressor.py

@@ -1,3 +1,5 @@
+"""Document compressor."""
+
 from __future__ import annotations
 
 from abc import ABC, abstractmethod

libs/core/langchain_core/documents/transformers.py

@@ -1,3 +1,5 @@
+"""Document transformers."""
+
 from __future__ import annotations
 
 from abc import ABC, abstractmethod