two intervals are equal if they contain the same elements, regardless of how `through` and `step` are stated: `interval 1 8 3 = interval 1 7 3` and `2..10:2 = interval 2 10 2`.
Complexity: O(1)
NOTE: two intervals with the same elements in opposite order are not equal, e.g. `1..10 ≠ 10..1:-1` — an `interval` compares as an ordered sequence, not as an unordered set.
regardless of how `through` and `step` are stated:
`interval 1 8 3 = interval 1 7 3` and `2..10:2 = interval 2 10 2`.
Complexity: O(1)
NOTE: two intervals with the same elements in opposite order are not
equal, e.g. `1..10 ≠ 10..1:-1` — an `interval` compares as an ordered
sequence, not as an unordered set.