fea: add isInRange extension

[guzishiwo]

 Returns true if this DateTime is in the range [start]-[end].
  [startInclusive] and [endInclusive] control the range boundaries:
- Left-open right-open (false, false): (start, end)
- Left-open right-closed (false, true): (start, end]
- Left-closed right-open (true, false): [start, end)
- Left-closed right-closed (true, true): [start, end]

[FMorschel]

Hello, @guzishiwo! Thanks for your PR!

It seems fine to me. I'd simply ask you to make more tests (for true and false for all cases of inclusive and exclusive). It can be rightfully implemented but we should be able to maintain it this way (if we ever need to refactor something) with more tests.

I'd also suggest you take a look at https://pub.dev/packages/due_date (https://github.com/FMorschel/due_date) which has a Period class that has this kind of tests (and some generators that take full days into account) and if you're willing, we can think of a wrapper class (on that package) that takes a Period and the booleans you have so we can test them in a similar way (maybe add an extension to facilitate the use).

I'm not sure what @jogboms thinks about having this on time, it seems a simple enough implementation for me. I'm not sure I'd personally do it with compareTo. If I did, I'd probably rename left and right to something more meaningful if I could think of anything, but it is hard since it returns an integer.