Make transaction a pytest fixture

[raxhvl]

A transaction is a function of fork. Often times fork specific transaction payload is constructed within a test.

        protected=False if fork in [Frontier, Homestead] else True,

A possible solution could be to make tx a pytest fixture (as pre is right now) which would allow automatic setting of the protected field based on the value of fork (which is also a pytest fixture). tx would have to be specified in the function arguments, as is pre right now.

it's a possible solution that would allow generalization of transactions for other chains, unlocking EEST for L2 EVM testing.

Originally posted by @danceratopz in #975 (comment)