fix(graphql): Consume streams from offline graphql requests

[elbieds]

Problem
GraphQL requests via the offline queueing system were not reaching the servers because the request streams were not being consumed.

Root Cause
The transmitRequest method in GraphqlOfflineRequestQueue was calling link.request(request) without consuming the returned stream.

Testing

1. Stream consumption test: Verifies that streams are properly consumed using Stream.eventTransformed to track when the stream is listened to
2. Error handling test: Ensures error streams are also consumed properly

Validation
Previously:

% dart test test/graphql_offline_request_queue_test.dart
00:00 +2 -1: GraphqlOfflineRequestQueue Request Processing #transmitRequest [E]                                           
  Expected: true
    Actual: <false>

00:00 +2 -2: GraphqlOfflineRequestQueue Request Processing #transmitRequest with errors [E]                               
  Expected: throws <Instance of 'Exception'>
    Actual: <Closure: () => Future<void>>

With the fix:

% dart test test/graphql_offline_request_queue_test.dart
00:00 +4: All tests passed!

[UrsDeSwardt]

LGTM 🎉