Implement Debug for vaults

src/simple.rs

@@ -13,6 +13,7 @@ use crate::{Action, Migration};
 /// This vault may be useful if you want to re-use existing [`Action`]s and
 /// [`Migration`]s but don't need the additional guarantees and overhead of the
 /// other vaults.
+#[derive(Debug)]
 pub struct SimpleVault(Connection);
 
 impl SimpleVault {

src/tokio.rs

@@ -86,7 +86,7 @@ fn run(mut conn: Connection, mut rx: mpsc::UnboundedReceiver<Command>) {
 }
 
 /// A vault for use with [`tokio`].
-#[derive(Clone)]
+#[derive(Debug, Clone)]
 pub struct TokioVault {
     tx: mpsc::UnboundedSender<Command>,
 }