This should reduce the memory usage of the application by dividing the size of unserialized transactions by 2, and saves a bytes.fromhex(..) conversion in the deserialization function.
The bytes.fromhex conversion now happens at the I/O layer (opening wallet files, receiving transactions from the network, copy-pasting unsigned hex transactions), where the conversion cost probably does not make a difference as the process is I/O bound.
Depends on D14525