slow tests in CI

[d-v-b]

The duration of tests in CI is approaching 9 minutes. In a recent run, these were the worst offenders in terms of test duration:

============================= slowest 10 durations =============================
29.98s call     zarr/tests/test_hierarchy.py::TestGroupV3WithABSStore::test_getitem_contains_iterators
21.72s call     zarr/tests/test_core.py::TestArrayWithABSStoreV3::test_resize_2d
19.63s call     zarr/tests/test_core.py::TestArrayWithABSStore::test_resize_2d
12.43s call     zarr/tests/test_storage.py::TestN5FSStore::test_s3_complex
12.34s call     zarr/tests/test_storage_v3.py::TestFSStoreV3::test_s3_complex
12.23s call     zarr/tests/test_storage.py::TestFSStore::test_s3_complex
10.55s call     zarr/tests/test_indexing.py::test_set_orthogonal_selection_3d
9.23s call     zarr/tests/test_hierarchy.py::TestGroupWithABSStore::test_getitem_contains_iterators
8.50s call     zarr/tests/test_core.py::TestArrayWithABSStoreV3::test_iter
8.45s call     zarr/tests/test_core.py::TestArrayWithABSStore::test_np_ufuncs
= 5042 passed, 191 skipped, 8 xfailed, 1 xpassed, 4 warnings in 510.00s (0:08:30) =

We could go after these slow tests, but we should also consider additional test refactors. I'm pretty sure we test a lot of things multiple times.

[joshmoore]

If there's a straight-forward fix for speeding up ABSStore, love to see it, but I imagine it may be more an issue of the set up we're using. If so, an option there might be to extract to a new repo (e.g. zarr-abststore).

test_s3_complex and test_set_orthogonal_selection_3d look more like they will have a straight-forward issue that needs addressing.

[jhamman]

Nearly all of these tests/stores were removed with 3.0 so I think we can safely close this.