Feature: Add Dual-Stack support with IPv6 preference

[devl00p]

Description

This PR modernizes the NICClient network logic by introducing Dual-Stack (IPv4/IPv6) support.

Previously, the library was forced to use socket.AF_INET (IPv4), making it unable to connect to WHOIS servers over IPv6 or leverage IPv6-only environments.

The core of this change is a refactoring of the connection logic into a centralized _connect method that uses socket.getaddrinfo with socket.AF_UNSPEC.

Key Changes

• Centralized Connection Logic: Introduced _connect(hostname, timeout) to handle DNS resolution and connection attempts. This replaces the scattered get_socket() + connect() calls in whois() and findwhois_iana().
• IPv6 Preference: Added a prefer_ipv6 toggle in NICClient.__init__. When enabled, the client sorts resolved addresses to prioritize AF_INET6 (IPv6) over AF_INET (IPv4).
• Robust Fallback (Happy Eyeballs-ish): If a connection to an IPv6 address fails (e.g., no route to host), the client automatically falls back to the next available address (IPv4) in the list.
• CLI Exposure: Added the --prefer-ipv6 flag to the command-line interface.

[richardpenman]

Thanks!