Port the ExpressTransport class and HTTP handling logic

Tasks:

• 2.1 Implement Python Transport interface/abstract base class
• 2.2 Port ExpressTransport class for chosen web framework
• 2.3 Implement request/response payload building functions
• 2.4 Port HTTP header parsing and BRC-104 compliance
• 2.5 Handle multipart/form-data and various content types
• 2.6 Implement response interception and modification