Python: Middleware sometimes produces 500 errors.

[hyacinthus]

https://github.com/coinbase/x402/blob/main/python/x402/src/x402/facilitator.py#L67

When this line calls VerifyResponse(**data), if a missing field is encountered, it generates a validation error. Since the upper layer does not catch the exception here, it causes the middleware to return an HTTP 500 error.