Update ERC-7930: define "Chain Identifier" term for zero-length-address IAs

[0xrcinus]

Summary

• Adds a Chain Identifier term to the Terminology section, defined as an Interoperable Address with a zero-length Address (i.e. one that identifies a chain rather than a specific address on that chain).
• References the new term in the AddressLength field description.
• Renames Example 4's heading from "Solana mainnet network, no address" to "Solana mainnet Chain Identifier".

Motivation

The spec already allows AddressLength == 0 (with ChainReferenceLength > 0) and demonstrates it in Example 4, but the construct had no name. Giving it a name ("Chain Identifier") makes it easier to refer to in downstream specs and conversation, and mirrors the existing Chain-specific Address term.

This change is purely additive terminology — no wire-format or semantic changes.

Test plan

• EIP linter passes
• Rendered markdown reads cleanly

🤖 Generated with Claude Code

[eip-review-bot]

✅ All reviewers have approved.

[eip-review-bot]

All Reviewers Have Approved; Performing Automatic Merge...