Add unit tests for socks_proxy.py

Summary

nettacker/core/socks_proxy.py currently has zero unit tests.
This file is critical, it's called directly in app.py for
every single scan via set_socks_proxy().

Affected File

nettacker/core/socks_proxy.py

What Needs to Be Done

Write unit tests covering:

• getaddrinfo() return format and structure
• set_socks_proxy(None) — no proxy, returns default socket
• set_socks_proxy("socks5://host:port") — SOCKS5 without auth
• set_socks_proxy("socks4://host:port") — SOCKS4 without auth
• set_socks_proxy("socks5://user:pass@host:port") — SOCKS5 with authentication

Place tests in tests/core/test_socks_proxy.py matching the existing pattern.

Acceptance Criteria

• All calls to socks library must be mocked (no real connections)
• 100% line coverage for socks_proxy.py
• Tests run successfully with pytest tests/core/test_socks_proxy.py

Context

This is part of the GSoC 2026 goal to raise overall test coverage to 85%.
The existing tests/core/test_die.py and tests/core/test_ip.py serve
as reference implementations.

Start with nettacker/core/socks_proxy.py and compare the patterns in tests/core/test_die.py and tests/core/test_ip.py. Run pytest tests/core/test_socks_proxy.py while adding mocked coverage for getaddrinfo() and each set_socks_proxy() case listed in the issue. Done means all socks-library calls are mocked, the requested cases pass, and socks_proxy.py reaches 100% line coverage.