chore: makes SyncReason public (as expected) (#1756)

## Description

`SyncReason` is a public enum, but it is never exported from its private
module.

We don't use `SyncReason` currently in the cli or console, but if other
applications have use for it, we need to make it public. Also, allows us
to using it in the ffi bindings.

iroh/src/sync_engine.rs

@@ -31,7 +31,7 @@ use gossip::GossipActor;
 use live::{LiveActor, ToLiveActor};
 
 pub use self::live::SyncEvent;
-pub use self::state::Origin;
+pub use self::state::{Origin, SyncReason};
 pub use iroh_sync::net::SYNC_ALPN;
 
 /// Capacity of the channel for the [`ToLiveActor`] messages.