[v3] slow tests

[d-v-b]

from my workstation:

================================================================================================================== slowest 10 durations ==================================================================================================================
9.17s call     tests/v3/test_indexing.py::test_set_orthogonal_selection_3d
1.98s call     tests/v3/test_indexing.py::test_set_orthogonal_selection_2d
0.71s call     tests/v3/test_indexing.py::test_set_orthogonal_selection_1d
0.61s call     tests/v3/test_indexing.py::test_get_orthogonal_selection_3d
0.49s call     tests/v3/test_store/test_remote.py::TestRemoteStoreS3::test_get[use_str-byte_range3--c/0]
0.46s call     tests/v3/test_indexing.py::test_set_coordinate_selection_2d
0.43s setup    tests/v3/test_store/test_remote.py::TestRemoteStoreS3::test_get[use_str-byte_range2-\x01\x02\x03\x04-foo/c/0.0]
0.43s call     tests/v3/test_store/test_remote.py::TestRemoteStoreS3::test_get[use_str-byte_range2--c/0]
0.42s setup    tests/v3/test_store/test_remote.py::TestRemoteStoreS3::test_get[use_str-None--foo/0/0]
0.42s setup    tests/v3/test_store/test_remote.py::TestRemoteStoreS3::test_get[use_str-None--foo/c/0.0]

We should alter test_set_orthogonal_selection_3d so that it runs faster. Not clear to me if this requires just changing the test suite or boosting zarr-python performance, or both.