Improve evmzero unit-testing.

[LuisPH3]

The interpreter unit test presents a series of issues:

It assumes instruction behavior is Istanbul unless other is specified. This assumption has leaked some untested behaviors, namely the different semantics for SELFDESTRUCT across Istanbul, Berlin, & London.
It is 5000+ plus lines, turns difficult to maintain. And it takes a long time to compile as well.

A replacement should, at least:

• Test the normal operation for each instruction on each Revision.
• Use fixtures/parametrized tests to avoid repetition. This could be tricky with Mocks.
• Multiple files

From @HerbertJordan feedback:

• it needs to be a structured approach; just having test defined for each pair of operation and revision is not sufficient; value-parameterized tests may be an option