feat: add rsFIRO Ethereum token

[reubenyap]

Summary

• add rsFIRO to the default Ethereum token list using the official contract address and 8 decimals
• let Campfire users add Firo and Ethereum wallets
• limit Campfire Ethereum token choices to rsFIRO, USDC, and USDT while keeping Stack Wallet behavior unchanged
• add missing default tokens to existing local token databases

Contract metadata: https://firo.org/2026/09/15/rsfiro-live.html

Testing

• GitHub Actions test job passes
• Dart formatting check passes
• default-token allowlist test covers the Campfire Ethereum tokens

CI: https://github.com/cypherstack/stack_wallet/actions/runs/35188999250/job/105097180090