v0.9.0 - Multi-Chain Escrow Support

Features:

• Add ESCROW_CONTRACTS registry with 9 EVM networks
• Networks: Base, Ethereum, Polygon, Arbitrum, Celo, Monad, Avalanche (mainnet + testnet)
• Auto-resolve contracts by chain_id in AdvancedEscrowClient
• New helpers: get_escrow_contracts(), get_supported_escrow_chains(), is_escrow_supported()
• Contract addresses from x402r-sdk multichain-config