Test: Added test cases for Download Documents HTTP API (#6032)

### What problem does this PR solve?

cover [download docments
endpoints](https://ragflow.io/docs/dev/http_api_reference#download-document)

### Type of change

- [x] add test cases

sdk/python/test/libs/utils/__init__.py

@@ -15,6 +15,7 @@
 #
 
 import base64
+import hashlib
 from pathlib import Path
 
 
@@ -23,3 +24,14 @@ def encode_avatar(image_path):
         binary_data = file.read()
     base64_encoded = base64.b64encode(binary_data).decode("utf-8")
     return base64_encoded
+
+
+def compare_by_hash(file1, file2, algorithm="sha256"):
+    def _calc_hash(file_path):
+        hash_func = hashlib.new(algorithm)
+        with open(file_path, "rb") as f:
+            while chunk := f.read(8192):
+                hash_func.update(chunk)
+        return hash_func.hexdigest()
+
+    return _calc_hash(file1) == _calc_hash(file2)