Separate schema from format

[kanarus]

closes #241

---

Before ohkami provided typed::{Query, Payload} for handling query parameters and payloads like

#[Payload(JSON/D)]
struct Hello<'req> {
    name: &'req str
}

#[Query]
struct HelloQuery {
    repeat: Option<usize>
}

but this enforces integrating format and schema, which is not modular or healthy.

---

For example, think about a case of maintaining a handler that takes a Hello<'_> as argument, and oneday you have to change the payload format from json into x-www-form-urlemcoded. In this situation with current Ohkami, you have to change

#[Payload(JSON/D)]
struct Hello<'req> ...

into

#[Payload(URLEncoded/D)]
struct Hello<'req> ...

this means you need to touch the struct definition, while the schema of payload is not changed.

Additionally, the handler definition

async fn handler(req: Hello<'_>, ...) -> ...

doesn't show clearly how it takes the data of type Hello<'_> ( and you have to go to the definition of Hello to know it ).

---

Now I think the responsibility of format ( query, json, urlencoded, ... ) should not owe to a struct in charge of the schema.

This PR removes typed::{Payload, Query} and introduces format module to separate schema from format:

#[derive(Deserialize)]
struct Hello<'req> {
    name: &'req str
}

#[derive(Deserialize)]
struct HelloMetadata {
    repeat: Option<usize>
}

use ohkami::format::{Query, JSON};

async fn handler(
    JSON(req): JSON<Hello<'req>>,
    Query(q): Query<HelloMetadata>,
    ...
) -> ...

[kanarus]

CI failed as I expected.
We have to wait cloudflare/workers-rs#619 to be merged and shipped.