Add txSize field to ShelleyTx and AlonzoTx.

[lehins]

There should be no reason why ShelleyTx retains the whole of original bytes, because it can't do so in a block anyways. The only reason why it uses MemoBytes is for size calculation needed for sizedTxF. Remove usage of MemoBytes for ShelleyTx, thus avoiding keeping around bytes for . However in order for us to memoize the size needed for computing the fee we should add a field to AlonzoTx and ShelleyTx. This will require creation of AlonzoTxRaw and removal of MemoBytes for ShelleyTx