Add properties to get chunk and shard slices

[dstansby]

Fixes #2454.

[d-v-b]

nitpicking the name: i find "slice" to be kind of ambiguous between a verb and a noun, and it also locks us in to returning slice objects, so what if we use the word "region" instead?

and also I think it's helpful if the name of this routine makes it clear that it's an iterator. So what if we call it iter_chunk_regions, i.e. the name of the routine it wraps 😜

[dstansby]

re. name, I think "slices" is unambiguously a noun because it's plural? I looked at NumPy (https://numpy.org/doc/stable/user/basics.indexing.html#slicing-and-striding), and they use the terms "index", "selection tuple", or "slicing tuple". If we try and stay consistent with NumPy, how about "chunk_indices"?

I like "regions", but to me it's ambiguous whether that means the index, or the array data at that index. If we settle on it that could be fixed by documentation and consistent use though.

re. iterator, do you mean generator? A list/string etc. are also iterators, but using a yield makes this into more specifically a generator.

So perhaps generate_chunk_indices? I find that a bit clunky though,

for chunk_index in arr.chunk_indices:

is much nicer than

for chunk_index in arr.generate_chunk_indices:

(or iter_chunk_indices)

which is why I prefer simply chunk_indices. I don't knkow if there's prior art in other libraries for naming generators?

[d-v-b]

generators are iterators, and my thinking was that putting "iter" in the name conveys that users should expect to iterate over the value returned by calling this method.

when I think of iterating over indices, I think of iterating over tuples of coordinates, e.g., (0, 0, 0), (0, 0, 1), .... which is what _iter_chunk_coords / _iter_shard_coords do right now.

[d-v-b]

I like "regions", but to me it's ambiguous whether that means the index, or the array data at that index. If we settle on it that could be fixed by documentation and consistent use though.

I worry that this ambiguity will hold for any name we pick :)

[codecov]

Codecov Report

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

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

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%)	⬇️

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