message: Make MockStorage debugable
diff: @@ -9,7 +9,7 @@ use crate::{FfiResult, ReadonlyStorage, Storage};
  #[cfg(feature = "iterator")]
  use cosmwasm_std::{Order, KV};
  -#[derive(Default)]
  +#[derive(Default, Debug)]
  pub struct MockStorage {
  data: BTreeMap<Vec<u8>, Vec<u8>>,
  }
  