feat: Add timeout logic to the x402 middleware

[arun-fairfetch]

In payments/x402.py, the middleware gates requests on payment. We need to ensure that if an agent hits a 402 challenge but fails to provide a proof or wallet token, the request doesn't hang the server resources during the handshake.

Task:

Locate the logic in payments/x402.py where it waits after calling the facilitator.

Implement a timeout mechanism to ensure slow agent responses don't cause bottlenecks.