Wrapper around NominalDiffTime with custom Arbitrary instance

The default Arbitrary instance for NominalDiffTime isn't very useful:

• It tends to pick huge values
• It tends not to pick integer values
• It does not shrink

Our custom instance

• Picks values between 0 and (1000 * 20 * 10) seconds:
• Maximum segment length: 1000
• Maximum slot length: 20 seconds
• Maximum number of segments: 10
• With a 0.1 second precision
• Shrinks

The tests for CumulEpochSizes requires that the sum of a list of these values does not overflow.

An epoch size must be > 0.

The functions slotAtTime and timeUntilNextSlot suffer from arithmetic overflow for very large values, so generate values that avoid overflow when used in these two functions. The largest value generated is still sufficently large to allow for 5e12 years worth of slots at a slot interval of 20 seconds.

Generate a small SlotNo for the state machine tests. The runtime of the StateMachine prop_sequential tests is proportional the the upper bound.

Picks time span between 0 seconds and (roughly) 50 years

Note - Arbitrary instance for NominalDiffTime comes from quickcheck-instances and it uses a much wider timespan.

Picks moment between dawnOfTime and (roughly) 50 years later

Note - Arbitrary instance for UTCTime comes from quickcheck-instances and it uses a much wider timespan.