I don't store any object coming from apollo_parser here because they are
!Send. This prevents the whole object to be moved to another thread.
This is why I need to create my own objects (enum Selection) which won't
have this limitation.

We won't serialize or deserialize on object creation because this
process is costly. So Request's `query` field stays a simple String and
Query becomes a new object more aware of the actual content of the
query.

Maybe I should have refactor that caching first...