add WalletRead::transaction_data_requests as unimplemented

[Oscar-Pepper]

solves build error:

error[E0046]: not all trait items implemented, missing: transaction_data_requests
  --> zingolib/src/wallet/tx_map_and_maybe_trees/trait_walletread.rs:57:1
   |
57 | impl WalletRead for TxMapAndMaybeTrees {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ missing transaction_data_requests in implementation
   |
   = help: implement the missing item: fn transaction_data_requests(&self) -> Result<Vec<TransactionDataRequest>, <Self as WalletRead>::Error> { todo!() }