allow int-like floats for int dtype fill values

[d-v-b]

Fixes #3447 by widening the permitted types of integer fill values to include "int-ish floats", e.g. 1.0 or 0.0.

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/user-guide/*.rst
• Changes documented as a new file in changes/
• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 61.06%. Comparing base (d3fa3f5) to head (07c9990).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/zarr/core/dtype/npy/common.py	25.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3448      +/-   ##
==========================================
- Coverage   61.07%   61.06%   -0.01%     
==========================================
  Files          79       79              
  Lines        9500     9506       +6     
==========================================
+ Hits         5802     5805       +3     
- Misses       3698     3701       +3     

Files with missing lines	Coverage Δ
src/zarr/core/dtype/npy/int.py	53.29% <100.00%> (+0.29%)	⬆️
src/zarr/core/dtype/npy/common.py	60.18% <25.00%> (-1.36%)	⬇️

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