Proto: consume less gas on empty transaction detection
A contract has code if and only if it is originated. Therefore,
there is no need to call Storage.Contract.Code.mem and
consume gas in order to detect forbidden empty transactions. As
a consequence, gas consumption is now reduced when crediting a
null amount to an originated contract.
Manually testing the MR
dune build @src/proto_alpha/lib_protocol/test/runtest
poetry run pytest tests_alpha/