Add MacAddress (net)

[vhrcgcom]

Description

Implement MacAddress as a ValueObject in the net module.

Spec: 6-byte MAC, normalised to lowercase colon-separated hex

Implementation checklist

• Create src/net/macaddress.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	MacAddressInput
Output	String — lowercase colon-separated, e.g. "aa:bb:cc:dd:ee:ff"	MacAddressOutput

Normalization

Strip all : and - separators; lowercase; then format as 6 pairs of hex digits separated by colons.

Validation

• After stripping separators, must be exactly 12 hexadecimal characters (6 bytes).

Extra methods

• bytes() -> [u8; 6] — the 6 raw bytes.
• is_broadcast() -> bool — true if all bytes are 0xff.
• is_multicast() -> bool — true if the least-significant bit of the first byte is 1 (IEEE multicast bit).

References

• ROADMAP.md
• CONTRIBUTING.md