Add `validate_between` for numbers and Time

Nobody has claimed this yet.

This would allow you to validate that either a number or a Time based column sits between some lower bounds and some upper bounds.

Something like this

```crystal
validate_between age, min: 30, max: 60
validate_between coupon, min: 2.days.ago, max: 2.days.from_now
```

We actually already have `validate_numeric` for validating that a number is within some range, so we could just make this for `Time` only, but I figure someone might reach for a number and wonder why it didn't work... We wouldn't get rid of `validate_numeric` though because with that you can set only a min or only a max and not care about the other bounds. With this you want to ensure that it's directly between the two.

Start by locating the existing validate_numeric implementation and read how validation bounds are represented and tested. Define the validate_between behavior for numeric and Time columns, including both required lower and upper bounds, and verify the example calls reject values outside the interval.

Written by the indexing model from the issue text.