[Testing] Add unit tests for core protocol libraries (HTTP, SSH, FTP, SMTP, Telnet, POP3)

Summary

The protocol handler libraries under nettacker/core/lib/ are almost entirely untested.
Out of 13 protocol files, only 3 have test coverage (SMB, SSL, Socket).
The remaining 10 — including HTTP, SSH, FTP, FTPS, SMTP, SMTPS, POP3, POP3S, Telnet, and Base —
have zero unit tests.

Affected Files

• nettacker/core/lib/base.py — base connection class (parent of all protocols)
• nettacker/core/lib/http.py — used by all scan/vuln modules
• nettacker/core/lib/ssh.py
• nettacker/core/lib/ftp.py / ftps.py
• nettacker/core/lib/smtp.py / smtps.py
• nettacker/core/lib/pop3.py / pop3s.py
• nettacker/core/lib/telnet.py

What Needs to Be Done

• Write unit tests for base.py covering connection lifecycle, timeout handling, and error states
• Write unit tests for http.py covering request building, response parsing, and condition matching (mock requests)
• Write unit tests for ssh.py covering auth attempts and error handling (mock paramiko)
• Write unit tests for ftp.py, ftps.py covering login flows and error handling (mock ftplib)
• Write unit tests for smtp.py, smtps.py covering connection and auth flows
• Write unit tests for pop3.py, pop3s.py
• Write unit tests for telnet.py
• Place tests in tests/core/lib/test_<protocol>.py matching the existing pattern

Acceptance Criteria

• All network calls must be mocked (no real connections)
• Each protocol file achieves ≥ 80% line coverage
• Tests run successfully with pytest tests/core/lib/

Context

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

Start with tests/core/lib/test_socket.py and test_smb.py, then inspect the protocol files under nettacker/core/lib/. Add matching tests under tests/core/lib/test_.py with all network calls mocked, and run pytest tests/core/lib/; done means the listed protocols reach at least 80% line coverage.