Core Payment Middleware Logic

[mo-jaber]

https://github.com/bsv-blockchain/py-middleware/milestone/8

Port the main payment processing functionality

Tasks:
Payment Middleware Class

createPaymentMiddleware() function to Python class
Implement request price calculation interface
Handle wallet integration and validation
Payment Flow Implementation

Implement 402 Payment Required response logic
Port BSV payment header parsing and validation
Handle derivation prefix creation and verification
Transaction Processing

wallet.internalizeAction() (Depends on WalletToolbox work below)
Implement payment result handling
Add proper error handling and status codes