Following up on zarrs/zarrs#53

1. Did validate_checksums ever need to be None, or is the change here to booleans ok?
2. Should we test that things don't error out on non-linux systems with direct_io flag set? I went with "no" and just skipped but would be fine testing it. I think this mimics the current zarrs behavior which seems to be "don't error out on and don't test on non-linux platforms"
3. I updated to zarrs 0.22.4 to pick up the new zarrs_filesystem which has O_DIRECT for reading