IntervalArray equality follow-ups 
Follow-ups to #30640 based on @jbrockmendel's comments.

Haven't addressed all the comments yet but pushing this up now so there's a record of it.

Changes thus far:
- Created `tests/arithmetic/test_interval.py ` and moved the tests there
- Used `make_wrapped_comparison_op` to add `__eq__` and `__ne__` to `IntervalArray`.