L402 Parser

Parses a single raw L402 string from an HTTP WWW-Authenticate header or DNS TXT record into a structured payment challenge object. Accepts one input: raw_input, the exact L402 header value or v=l402 TXT content. You must interpret the raw_input string, extract L402 fields and parameters, and map them into the fields defined by the system-provided structured output schema. The final response must be only JSON and must strictly validate against that system-provided structured output schema with correct field names, types, enums, and no extra keys.