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

Author: notmandatory

crates/bdk/src/wallet/mod.rs

@@ -257,7 +257,12 @@ impl Wallet {
                 NewError::Write(_) => unreachable!("mock-write must always succeed"),
             })
     }
+}
 
+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`].