Add test for block timestamps

[Wodann]

Hardhat used to have tests to validate the timestamp logic in HardhatNode. These tests used SinonFakeTimers to manually manipulate the observed system clock.

This can not be achieved in the same way but instead requires a refactor of EDR to support an interface for determining the block's timestamp. As such, these tests were not ported when ethereumjs was replaced.

Definition of Done

• Refactor EDR to receive a trait (object) for determining the block's timestamp
• Add tests based on Hardhat tests that validate block timestamp calculation