Breaking updates to the Fixture Formats

[marioevz]

          ok since we changin the state format anyway. I have rather radical proposal. 

if it is 1 test per file now. then it could have network field as blockchain test.
an no need to create subdict of cancun here and in other places.
and post can be postState directly without list of forks.
and transaction could have no arrays. and indexes field will be removed in post state

Originally posted by @winsvega in #1040 (comment)

[winsvega]

1 test per file I mean 1 logical test. It can still be a json array of test-frontier, test-cancun.

The idea is to revert transaction vectors from state tests