Refactor DateTime and Duration tests to use chain.assertOK

[gavv]

DateTime and Duration have many fragments like this:

			if tc.expectInRange {
				NewDateTime(reporter, tc.value).
					InRange(tc.min, tc.max).
					chain.assertNotFailed(t)
			} else {
				NewDateTime(reporter, tc.value).
					InRange(tc.min, tc.max).
					chain.assertFailed(t)
			}
			if tc.expectNotInRange {
				NewDateTime(reporter, tc.value).
					NotInRange(tc.min, tc.max).
					chain.assertNotFailed(t)
			} else {
				NewDateTime(reporter, tc.value).
					NotInRange(tc.min, tc.max).
					chain.assertFailed(t)
			}

With recently added chain.assertOK, such fragments can be simplified to:

			NewDateTime(reporter, tc.value).InRange(tc.min, tc.max).
				chain.assertOK(t, tc.expectInRange)

			NewDateTime(reporter, tc.value).NotInRange(tc.min, tc.max).
				chain.assertOK(t, tc.expectNotInRange)

This should be done in all appropriate tests in datetime_test.go and duration_test.go.

Similar to #345

[Darrellbor]

@gavv I'd like to work on this

[gavv]

Do you ever sleep? :) You're welcome!

[Darrellbor]

@gavv 😂 I do, I've been trying to get my golang prowess to the level of my javascript/typescript
plus coding is somewhat soothing for me 😂