This fixes a bug where the Zod-parsed request
body accessed via `req.json()` had potentially
incorrect types due to JSON serialization. Now
the `json()` method is overridden so that the parsed
data is returned as is without the JSON serialization.

Additionally, the request path parameters are now also
validated when using app router when previously they
were used only for providing types for the used path
parameters.

This change serializes Blob data for API routes
and creates a JSON object from form responses,
although these are rare cases.