Verify a claimed USDC payment on Base: given a tx hash (or an x402 PAYMENT-RESPONSE header) and what you expect (payee, payer, amount, time window, confirmations), reads the chain and returns match / mismatch / not_settled / not_found with per-field checks, finality, the x402 EIP-3009 pattern, a self-payment flag and a second-RPC cross-check. Cannot show who owns an address or that a service was d