Refactor SubjectsEndpoint to DRY up filtering logic

Collapsed duplicated site filtering logic in `SubjectsEndpoint` into a shared `_filter_by_site` method. This improves maintainability and ensures consistent behavior between synchronous and asynchronous operations.

Verified with new unit tests covering both execution paths.

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

Author: fderuiter

tests/unit/endpoints/test_subjects_filtering.py

@@ -1,19 +1,23 @@
-import pytest
-from unittest.mock import Mock, AsyncMock
 from typing import List
+from unittest.mock import AsyncMock, Mock
+
+import pytest
+
 from imednet.endpoints.subjects import SubjectsEndpoint
 from imednet.models.subjects import Subject
 
+
 @pytest.fixture
 def subject_list():
     return [
         Subject(studyKey="sk", subjectId=1, siteId=101, subjectKey="s1"),
         Subject(studyKey="sk", subjectId=2, siteId=102, subjectKey="s2"),
         Subject(studyKey="sk", subjectId=3, siteId=101, subjectKey="s3"),
-        Subject(studyKey="sk", subjectId=4, siteId="101", subjectKey="s4"), # String siteId
+        Subject(studyKey="sk", subjectId=4, siteId="101", subjectKey="s4"),  # String siteId
         Subject(studyKey="sk", subjectId=5, siteId="103", subjectKey="s5"),
     ]
 
+
 def test_list_by_site_filtering(subject_list):
     # Mock client and context as they are required by __init__ but not used if we mock list
     mock_client = Mock()
@@ -36,6 +40,7 @@ def test_list_by_site_filtering(subject_list):
 
     assert len(filtered_mismatch) == 0
 
+
 @pytest.mark.asyncio
 async def test_async_list_by_site_filtering(subject_list):
     # Mock client and context