Interface hasn't been unified between HTTP and graphsync

[willscott]

The final Syncer interface is defined, but the interface for creating a Sync vs Syncer, and then getting a Syncer from the Sync object has diverged a lot between the two paths.
It should be as easy as having the needed host or http client available, and getting the right syncer based on the type of addr-info passed in.

[gammazero]

I think this is closer now, but not sure if sufficient to close this:
https://github.com/filecoin-project/go-legs/blob/main/subscriber.go#L676
https://github.com/filecoin-project/go-legs/blob/main/subscriber.go#L693