[codex] add zone RPC URL metadata

[danrobinson]

Summary

• add ZonePortal zoneRpcUrl storage plus setZoneRpcUrl(string) with ZoneRpcUrlUpdated(address indexed updater, string newZoneRpcUrl)
• allow empty strings, cap URLs at 256 bytes, require an ASCII-case-insensitive https scheme, and intentionally do not validate after the first : to mirror the TIP-1026 scheme-validation style
• thread the URL through ZoneFactory.createZone, ZoneCreated, ZoneInfo, Rust ABI bindings, create-zone, zone-info, and a new set-zone-rpc-url xtask/Just recipe

Validation

• cargo check -p zone-primitives -p tempo-xtask
• forge build --skip test
• forge test --match-path 'test/zone/Zone{Factory,Portal}.t.sol' currently compiles, then fails in local test setup because this machine’s forge does not recognize the repo’s Tempo hardfork/precompile config: MissingPrecompile("AccountKeychain", 0xaAAAaaAA00000000000000000000000000000000).