EIP-155 (EVM) chain support for the x402 payment protocol.

Exact scheme: ERC-3009 transferWithAuthorization and Permit2 via x402ExactPermit2Proxy. Upto scheme: Permit2 witness via x402UptoPermit2Proxy (verify = max, settle = actual ≤ max). EIP-1271 / EIP-6492 smart-wallet signatures are accepted on verify and settle. Insufficient Permit2 allowance is [r402_protocol::error::VerificationError::Permit2AllowanceRequired] (HTTP 412). Also implements auth-capture and batch-settlement.

Features

• server — [Eip155Exact::price_tag], [Eip155Upto::price_tag]
• client — [Eip155ExactClient] / [Eip155UptoClient] EIP-712 signing
• facilitator — [Eip155ExactFacilitator::try_new], [Eip155UptoFacilitator::try_new]
• telemetry — tracing spans on RPC paths