defines blocksize for array, updates hexdigest values

[andrewfulton9]

[Description of PR]
Should fix partial read test by defining blocksize for Blosc compression.

related to conversation in #859

TODO:

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions
• New/modified features documented in docs/tutorial.rst
• Changes documented in docs/release.rst
• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)

[codecov]

Codecov Report

Merging #867 (95bcdbd) into master (a92550b) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #867   +/-   ##
=======================================
  Coverage   99.94%   99.94%           
=======================================
  Files          32       32           
  Lines       11204    11204           
=======================================
  Hits        11198    11198           
  Misses          6        6           

Impacted Files	Coverage Δ
zarr/tests/test_core.py	100.00% <100.00%> (ø)

[joshmoore]

Wow. Thanks, @andrewfulton9! I'll merge this and try to get all the related conversations green. We might need to review use of Blosc() especially:

(base) /opt/zarr-python $git grep -nE "Blosc\(" zarr/storage.py
zarr/storage.py:80:    default_compressor = Blosc()

[joshmoore]

released on the 2.10 line: https://zarr.readthedocs.io/en/stable/release.html#release-2-10-3