Split route handlers and operations

[tk-o]

The goal is to have route handlers to call operations, where operations return a Result object instance.

Here's the idea shared by @lightwalker-eth about moving our API handlers into 2 distinct layers of responsibility:

1. All the deserialization / serialization / input validation.
2. The actual business logic -- where there's beautifully typed params and response.

Hono calls directly into 1, which would then call into 2 only after deserialization / input validation is complete.