Test/test execution state

[18aaddy]

Resolves #75
Written tests for execution/state.go

• Written tests for all functions
• Working locally (all tests passing)

I haven't written tests separately for PushBlock and PushFinalizedBlock as they are already covered in other tests

[18aaddy]

The lint test is failing because of a for loop
for state.finalizedBlock == nil {}
This is needed as it waits for the finalized block to be pushed before continuing. If it doesn't wait, it could lead to unexpected results.
This is only a warning at compilation time, not an error