Reconsider empty interval contains

[electronjoe]

It seems it would be more mathematically consistent to state that the empty interval contains the empty interval. Consider making this change.

            // The Empty Interval contains no other Intervals (even Empty)
            (Bound::None, _) => false,

[electronjoe]

Alternatively:

Consider adding a subset_of method alongside contains to better align with mathematical convention. This would allow ∅ ⊆ ∅ while maintaining the current strict containment semantics.