no overlapping availabilities

[ooddaa]

Hi Karoline 👋

Thanks for your blogpost Building a nested, dynamic form in LiveView which was very helpful and aided my understanding of using cast_assoc/3 to build nested LV forms.

I decided to dig a bit deeper and see if I could contribute something.

There is a missing required feature:

• Not be able to add overlapping interview availabilities for the same day.

I have created a PR with my implementation and tests of this feature. I would greatly appreciate if you could review it and let me know your thoughts.