Add methods returning just the deserializer

[elrafoon]

Hello,

please accept this pull request, it allow user to use seeded deserializers, like this:

let des = AuthListDeserializer {
    auth_entry_visitor: Some(|e: AuthListEntry| println!("{e:?}")),
};

let file_in = std::fs::OpenOptions::new().read(true).open(pth)?;
let mut scratch = [0u8; 16];
let auth_list = des.deserialize(&mut ciborium::de::deserializer_from_reader_with_buffer(file_in, &mut scratch))?;

[rjzak]

@elrafoon please run cargo fmt, otherwise, looks good to me.

[elrafoon]

I ran cargo fmt --all, several times, it did nothing. Also cargo fmt --check passed.

Don't know what's wrong.

[elrafoon]

Thanks!