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`.
LGTM Thanks @jschendel  @jschendel could IntervalIndex also pass through inequalities to IntervalArray?  if so then thats some more code we can share Yes, although inequalities haven't been implemented yet, even at the scalar `Interval` level.  Still would be good to get the code to share in place though, as the error messages are inconsistent.