feat: structure composition errors

[EverlastingBugstopper]

Regular composition error output now uses proper std::error::Error implementations with chains of errors rather than the previous iteration where we just hacked in a bunch of calls to eprintln!

Checking the proposed schema for subgraph users against rover-supergraph-demo@current
error[E029]: Encountered 1 composition error while trying to compose subgraph "users" into supergraph "rover-supergraph-demo@current".

Caused by:
    KEY_FIELDS_SELECT_INVALID_TYPE: [users] User -> A @key selects emaillll, but User.emaillll could not be found
    
              The changes in the schema you proposed for subgraph users are incompatible with supergraph rover-supergraph-demo@current. See https://www.apollographql.com/docs/federation/errors/ for more information on resolving composition errors.

This PR also includes a custom serializer for our error struct that will include structured composition errors if they have occurred, whether they are detected on a subgraph check or a supergraph compose.