feat: allow passing stings with units in function calls and transfers

[willemneal]

Now you can pass strings like 1 N when using function calls and transfers. E.g.

  await root.call(
    ft,
    'ft_transfer_call',
    {
      receiver_id: defi,
      amount: transferAmount,
      memo: null,
      msg: 'take-my-money',
    },
    {attachedDeposit: '1 yN', gas: '150 Tgas'},
  );