refactor(wallet): put get_address and get_internal_address into infallible impl block

Author: notmandatory

crates/bdk/src/wallet/mod.rs

@@ -226,7 +226,12 @@ impl Wallet {
             NewError::Persist(_) => unreachable!("no persistence so it can't fail"),
         })
     }
+}
 
+impl<D> Wallet<D>
+where
+    D: PersistBackend<ChangeSet, WriteError = core::convert::Infallible>,
+{
     /// Infallibly return a derived address using the external descriptor, see [`AddressIndex`] for
     /// available address index selection strategies. If none of the keys in the descriptor are derivable
     /// (i.e. does not end with /*) then the same address will always be returned for any [`AddressIndex`].