Add properties to get chunk and shard slices

[dstansby]

Fixes https://github.com/zarr-developers/zarr-python/issues/2454.

[codecov[bot]]

Codecov Report

:x: Patch coverage is 30.76923% with 9 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 61.83%. Comparing base (c8d8e64) to head (f5ea95a). :warning: Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/zarr/core/array.py	30.76%	9 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3573      +/-   ##
==========================================
- Coverage   61.87%   61.83%   -0.04%     
==========================================
  Files          85       85              
  Lines       10134    10146      +12     
==========================================
+ Hits         6270     6274       +4     
- Misses       3864     3872       +8     

Files with missing lines	Coverage Δ
src/zarr/core/array.py	68.18% <30.76%> (-0.44%)	:arrow_down:

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