Type checking fails when using constructor overrides in arrayconnection.py

[markedwards]

Overriding one of the type constructors in one of the resolvers in arrayconnection.py breaks the return type of resolver.

For instance:

@dataclass
class CustomConnection:
    edges: List[Edge]
    pageInfo: PageInfo

# connection is typed as Connection, but it is actually CustomConnection
connection = connection_from_array(
    [], 
    connection_type=CustomConnection,
)

As with issue #29, this can be cleanly resolved using custom Protocol definitions, although there is the downside noted in that issue of the additional typing-extensions dependency.

Unlike the other issue, I think you could implement a partial solution using Callable, TypeVar, and overload from typing, without having the Protocol dependency. I'm pretty sure the resulting code would be extremely difficult to understand though, and it would be very verbose.

[markedwards]

As with #29, I'm adding a PR here to demonstrate a solution using Protocol. Even if this is deemed unpalatable right now, it be an acceptable change in the future.