Overlap bug in struct closed_adjacent issue with unsigned indexes

[lailoken]

This code will not work due to the - 1 on l2 (which can be unsigned).
Possibly just + 1 on h1 rather?

        static inline bool overlaps(numerical_type l1, numerical_type h1, numerical_type l2, numerical_type h2)
        {
            return (l1 <= (h2 + 1)) && ((l2 - 1) <= h1);
        }

[lailoken]

Unsigned errors like these are commonly missed! (and led me on a merry goose chase!)
(I just created my own coverage struct with the fix.)

[5cript]

I am slightly afraid that unsigned is not going to work with lots of things. I have searched for -1 and some builtin interval types also dont respect unsigned properly.
I hope that all of these can be fixed within the provided interval structs and there are no issues in the tree class. Will have to eye scan through it for this issue.

[lailoken]

I did some rudimentary tests with the functions I'm using and it ostensibly worked. But I understand that not all code paths may have been hit.
I appreciate the rigor.

[5cript]

I hope I got everything with #53

I also decided not to care about overflow/underflow in signed cases or super large numbers, that is unreasonable.
I also assume that (high - low) is always >= 0, otherwise the interval is invalid, I do not intend to support anitmatter intervals, its complicated enough as is :D