Revert change to delta filter

[dstansby]

This reverts #584, as it has caused two issues so far, one of which is unresolved: #653 and #595.

There is a proposed fix at #657, but that is held up under review.

In order to un-break zarr-python, I think reverting here is the right thing to do (so we can do a 0.15 release with other stuff).

My intention is to add a test to #653 to this PR too, so keeping as draft. Opening so there's time for folks to see that I'm intending to do this; cc @jakirkham @ehgus

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.70%. Comparing base (f005306) to head (fea7eda).
Report is 31 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #677      +/-   ##
==========================================
- Coverage   99.70%   99.70%   -0.01%     
==========================================
  Files          62       62              
  Lines        2753     2751       -2     
==========================================
- Hits         2745     2743       -2     
  Misses          8        8              

Files with missing lines	Coverage Δ
numcodecs/delta.py	100.00% <100.00%> (ø)

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[ehgus]

I hope PR #657 will be reviewed soon as it fixes issue #653, which was caused by unsafe casting. In addition, this PR includes improved tests, so it will be glad someone feedback #657. Thank you for the remind.