test: Count only session seeks in retry seek test

Patch out MultipartStream, which sizes file streams itself, so the test
checks that the session rewinds file streams before each attempt without
depending on how the generated encoder measures them.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: congminh1254

test/boxsdk/unit/session/test_session.py

@@ -1,5 +1,5 @@
 from functools import partial
-from io import IOBase, BytesIO, SEEK_END
+from io import IOBase, BytesIO
 from numbers import Number
 import os
 from unittest.mock import MagicMock, Mock, PropertyMock, call, patch, ANY
@@ -264,16 +264,20 @@ def test_box_session_seeks_file_after_retry(
     mock_file_2.tell.return_value = 3
     files = {'file': ('unused', mock_file_1), 'f2': ('unused', mock_file_2)}
 
-    box_response = box_session.post(url=test_url, files=files)
+    # the multipart encoder sizes the streams itself, so only count the session's seeks
+    with patch('boxsdk.session.session.MultipartStream'):
+        box_response = box_session.post(url=test_url, files=files)
     assert box_response.status_code == 200
     assert box_response.json() == generic_successful_response.json()
     assert box_response.ok == generic_successful_response.ok
     mock_file_1.tell.assert_called_with()
     mock_file_2.tell.assert_called_with()
-    # before each attempt the session rewinds the stream, then the multipart
-    # encoder measures its size and restores the position
-    assert mock_file_1.seek.call_args_list == [call(0), call(0, SEEK_END), call(0)] * 2
-    assert mock_file_2.seek.call_args_list == [call(3), call(0, SEEK_END), call(3)] * 2
+    mock_file_1.seek.assert_called_with(0)
+    assert mock_file_1.seek.call_count == 2
+    mock_file_1.seek.assert_has_calls([call(0), call(0)])
+    mock_file_2.seek.assert_called_with(3)
+    assert mock_file_2.seek.call_count == 2
+    mock_file_2.seek.assert_has_calls([call(3), call(3)])
 
 
 def test_box_session_raises_for_non_json_response(