fix: resolve all Ruff linting errors

- Fix PLW2901: Use different variable name for stripped lines in loop
- Fix E721: Use 'is' instead of '==' for type comparisons
- Add noqa comments for intentional security warnings (S321, S507, S110, S603)

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

tests/test_upload_email.py

@@ -1,11 +1,8 @@
 """Tests for app/tasks/upload_to_email.py module."""
 
 import json
-import os
-import smtplib
 import socket
 from email.mime.multipart import MIMEMultipart
-from pathlib import Path
 from unittest.mock import MagicMock, Mock, mock_open, patch
 
 import pytest