Add IpV6Address (net)

[vhrcgcom]

Description

Implement IpV6Address as a ValueObject in the net module.

Spec: valid IPv6

Implementation checklist

• Create src/net/ipv6address.rs
• Implement ValueObject trait
• Add #[cfg_attr(feature = "serde", derive(serde::Serialize, serde::Deserialize))]
• Export from src/net/mod.rs and prelude
• Unit tests: valid input · empty input · invalid format · normalisation
• Doc comment with # Example block
• Update status in ROADMAP.md from ⬜ to ✅

Implementation detail

Input / Output

	Type	Alias
Input	String	IpV6AddressInput
Output	String — canonical lowercase with :: compression	IpV6AddressOutput

Normalization

Parse with std::net::Ipv6Addr, then re-serialise to its Display form (canonical lowercase with :: compression where applicable).

Validation

Must parse successfully via std::net::Ipv6Addr::from_str.

Extra methods

• segments() -> [u16; 8]
• is_loopback() -> bool — true for ::1.

References

• ROADMAP.md
• CONTRIBUTING.md