`vXY::wallet` has concrete bitcoin type

[tcharding]

v19::wallet should have String not Transaction

    /// The decoded transaction (only present when `verbose` is passed). v19 and later only.
    pub decoded: Option<Transaction>,

And v20, v23, v24, v26, v28

[tcharding]

Just throw

        let decoded = self.decoded.map(|tx| encode::deserialize_hex::<Transaction>(&tx).map_err(E::Tx)).transpose()?;

in the GetTransaction::into_model impl.