backend: mark BackendError::Other as transparent

The inner error should be the source, and I don't think the "Error:" prefix
gives additional context.

lib/src/backend.rs

@@ -217,7 +217,7 @@ pub enum BackendError {
         object_type: &'static str,
         source: Box<dyn std::error::Error + Send + Sync>,
     },
-    #[error("Error: {0}")]
+    #[error(transparent)]
     Other(Box<dyn std::error::Error + Send + Sync>),
 }