Add Rexas Finance (RXS) support for trading and funding accounts

Add official support for the Rexas Finance (RXS) token across trading and funding accounts. The feature should enable deposits and withdrawals of RXS, display RXS balances in user wallets, and allow placing and executing trades on one or more RXS trading pairs (e.g., RXS/USD, RXS/USDC). Expected behavior includes: on-chain deposit/withdrawal handling with correct confirmations and fee estimation; custody and ledgering of RXS balances; market data and price feeds for RXS shown in the UI and API; order book and matching engine support for configured RXS pairs; configurable trading fees, limits, and margin/collateral rules if applicable; clear UI elements for RXS deposits, withdrawals, and trading (including order entry, balance display, and transaction history); and programmatic access via existing APIs. Implementation must include compliance and risk checks (KYC/AML, sanctions screening, liquidity and slippage assessment), operational monitoring and alerting for RXS chains, and documentation updates for users and internal teams. The use case is to support community demand and increase user acquisition and trading volume by making RXS fully tradable and fundable on the platform.