community: better support of pathlib paths in document loaders (#18396)

So this arose from the
https://github.com/langchain-ai/langchain/pull/18397 problem of document
loaders not supporting `pathlib.Path`.

This pull request provides more uniform support for Path as an argument.
The core ideas for this upgrade: 
- if there is a local file path used as an argument, it should be
supported as `pathlib.Path`
- if there are some external calls that may or may not support Pathlib,
the argument is immidiately converted to `str`
- if there `self.file_path` is used in a way that it allows for it to
stay pathlib without conversion, is is only converted for the metadata.

Twitter handle: https://twitter.com/mwmajewsk

libs/community/langchain_community/document_loaders/evernote.py

@@ -5,8 +5,9 @@ https://gist.github.com/foxmask/7b29c43a161e001ff04afdb2f181e31c
 import hashlib
 import logging
 from base64 import b64decode
+from pathlib import Path
 from time import strptime
-from typing import Any, Dict, Iterator, List, Optional
+from typing import Any, Dict, Iterator, List, Optional, Union
 
 from langchain_core.documents import Document
 
@@ -35,9 +36,9 @@ class EverNoteLoader(BaseLoader):
             the 'source' which contains the file name of the export.
     """  # noqa: E501
 
-    def __init__(self, file_path: str, load_single_document: bool = True):
+    def __init__(self, file_path: Union[str, Path], load_single_document: bool = True):
         """Initialize with file path."""
-        self.file_path = file_path
+        self.file_path = str(file_path)
         self.load_single_document = load_single_document
 
     def _lazy_load(self) -> Iterator[Document]: