feat: gsmol-compatible backup export and import behind the store feature

core/src/lib.rs

@@ -11,6 +11,10 @@ pub mod address;
 pub mod client;
 pub mod crypto;
 pub mod error;
+// The gsmol export format is sealed mail plus the store's trust rows, so it
+// exists only alongside the store.
+#[cfg(feature = "store")]
+pub mod export;
 pub mod message;
 #[cfg(feature = "rns")]
 pub mod rns;