Fix [UseConnection] source generation for resolvers returning Connection<T>

[PHILLIPS71]

[UseConnection] on a source generated resolver only worked for PageConnection<T>. Returning Task<Connection<T>> (the type the common DataLoader pattern ToConnectionAsync() produces) was broken two different ways:

1. The generator did not recognize Connection<T> as a connection, because IsConnectionType only matched types deriving from ConnectionBase<,,>. The field ended up typed as a plain list with no paging arguments.

2. Once recognized, the generator built the connection type by reflecting over Connection<T>'s public members. That produced code that does not compile (a bogus resolver for Accept(IPageObserver)) and the wrong schema shape: no nodes field, info instead of pageInfo, and an edge type missing cursor (interface base members aren't reachable through BaseType).

Fix

Mirror the split the runtime already uses for [UsePaging]: a shared generic connection type for plain Connection<T>, reflection based named types only for custom classes.

• IsConnectionType now matches IConnection<T> implementors, a superset of the old ConnectionBase<,,> check.
• When a resolver returns exactly Connection<T> or IConnection<T>, ConnectionTypeTransformer skips type synthesis and the generated code binds the field to the existing shared runtime ConnectionType through a new helper, ConnectionTypeHelper.CreateConnectionTypeReference. This gives correct edges { cursor node }, nodes, pageInfo, and totalCount with no reflection over the connection class.
• PageConnection<T> and custom connection classes keep the existing reflection path.
• Reflection based synthesis now skips void returning methods, so custom subclasses of Connection<T> can't hit the Accept compile error either.