Harden network scans and fix DNS lookup

[PaulMass]

Motivation

• Reduce failed runs and risky inputs by validating target addresses, IP ranges and port specifications before performing network scans.
• Fix DNS lookup usage by importing the correct socket symbol and remove an unused dependency to simplify installs.
• Update documentation and requirements to reflect the new input validation behavior and dependency changes.

Description

• Added port validation with PORTS_PATTERN and _is_valid_ports and hostname/IP validation with _is_valid_target in network_scanner.py, and used them in port_scan to reject invalid inputs.
• Added CIDR validation in arp_scan using ipaddress.ip_network to reject invalid IP ranges before sending ARP requests.
• Imported socket in info_analysis.py to support dns_lookup and removed the unused requests import, and added a whois import in main.py to support Whois type checks.
• Removed requests from requirements.txt and added a short note in README.md about input validation for scans.

Testing

• No automated tests were run for these changes.

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Codex Task