SyncResult should not have "Result" in the name

[LLFourn]

A "Result" type in rust is conventionally always meant to be a enum with an error variant.

This should be called SyncResponse since it is what you get after sending a SyncRequest.

The present name should be deprecated and type alias to SyncRequest.

[notmandatory]

This is only a low-risk rename so I'd like to get it in with 1.0 rather than creating the type alias.