test(asset-registry): register xcFOON from Taifoon

[yawningmonsoon]

Summary

Adds an integration test for accepting xcFOON — the native currency of Taifoon (a Polkadot parachain, Moonbeam fork) — into Hydration's asset registry.

Draft. Taifoon is not yet registered on Polkadot, so TAIFOON_PARA_ID is a placeholder (3369) pending its real reserved para id. In production the actual integration is not a code change — it's an on-chain assetRegistry.register submitted via a GeneralAdmin OpenGov referendum. This PR adds the test that mirrors that call so the round-trip is covered in CI.

The multilocation (the load-bearing detail)

Taifoon is a Moonbeam fork, so xcFOON uses the Moonbeam-family shape — PalletInstance(10) (Balances/native, 18 decimals), not GeneralIndex:

AssetLocation(Location {
    parents: 1,
    interior: [Parachain(TAIFOON_PARA_ID), PalletInstance(10)].into(),
})

Changes

• integration-tests/src/polkadot_test_net.rs: TAIFOON_PARA_ID const (placeholder).
• integration-tests/src/asset_registry.rs: root_should_register_xcfoon_from_taifoon — registers xcFOON via AssetRegistry::register (18 decimals, AssetType::Token) and asserts location_assets / locations round-trip. Mirrors the existing root_should_update_location_when_asset_exists pattern and the AssetType usage in evm.rs.

Also required for full integration (relay-chain governance, not this repo): bidirectional HRMP Taifoon↔Hydration via hrmp.hrmpInitOpenChannel/hrmpAcceptOpenChannel.

[yawningmonsoon]

Closing to complete internal review first — Taifoon's para id isn't reserved yet (the test uses a placeholder). Will reopen when the real para id + HRMP are in place. Apologies for the premature draft.