Assert no underflow/overflow happened with UInt64 in tests

[mkalinin]

Background

There is a bunch of consensus types derived from UInt64 like SlotNumber, EpochNumber, ShardNumber, etc. Variables of these types could get underflowed or overflowed during various calculations. It would be nice to catch these cases all over the code in tests.

To Do

Implement a flag that would enable assertion that no underflows/overflows happens in UInt64 variables and its derivatives. Set this flag to false by default and enabled it only when JUnit tests takes the scene.