Dynamic interval `overlaps` can result in integer overflow

[whimxiqal]

Using dynamic-type interval overlaps can result in integer overflow when the boundaries of the intervals are maximum integers due to indiscriminate addition

external/+cc_libraries+interval-tree/include/interval-tree/interval_types.hpp:423:41: runtime error: signed integer overflow: 9223372036854775807 + 1 cannot be represented in type 'long int'

[5cript]

Fixed by #60