Fix Python linting issues in iptables test file

Fixed all ruff linting issues:
- Removed unused yaml import
- Fixed import sorting (pathlib before third-party imports)
- Removed trailing whitespace from blank lines
- Added newline at end of file

All tests still pass after formatting fixes.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

tests/unit/test_iptables_rules.py

@@ -6,9 +6,9 @@ These tests verify that the iptables rules templates generate correct
 NAT rules for both WireGuard and IPsec VPN traffic.
 """
 
-import pytest
-import yaml
 from pathlib import Path
+
+import pytest
 from jinja2 import Environment, FileSystemLoader