Add `into_tuple` to `SelectTwo` and `SelectTwoMany`

Motivation

Currently into_tuple only works on single Select queries. This leads to inconsistencies between the different query types and as such it should be extended to support the SelectTwo and SelectTwoMany queries.

Code like this should work

let res = Email::find_by_id(email_id)
        .select_only()
        .find_also_related(Thread)
        .column(thread::Column::Id)
        .into_tuple()
        .one(db)
        .await?;

Proposed Solutions

into_tuple should work the same as it currently does with Select

Current Workarounds

Currently you can query normally and get a struct in return but getting a tuple directly could help reduce code verbosity.

Start by locating the existing into_tuple implementation for Select, then inspect the SelectTwo and SelectTwoMany query entry points. Compare their behavior with Select and identify the relevant tests or examples for tuple results. Done means the shown find_also_related query can call into_tuple and return the expected tuple result.