Include translations in multiscales

[will-moore]

Fixes #403.

This is on top of #515. Can rebase once that's merged.

Encouraged by discussion at ome/ngff#89 (comment), this adds translation to the dataset coordinateTransformsations generated on downsampling.

Need to add/update tests...

cc @jo-mueller

[almarklein]

BTW, with the 'nearest' downsample method, I imagine it basically does a[::2] for all dimensions; the new samples are exactly on top of the samples in the previous layer. This gives the following scheme, and the offsets should be zero:

             _______ _______ _______ _______
            |___o___|___o___|___o___|___o___|   level 0
         _______________ _______________ ___
        |_______o_______|_______o_______|___    level 1
 _______________________________ ___________
|_______________o_______________|___________    level 2

Edit: nevermind, with nearest it does not matter which of the two pixels is taken, so in this case the offset can be either, I guess. That said, if you first smooth the data and then sample it with a[::2] the above schema does apply, because you've moved information from the neighbours to the sampled pixels.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.67%. Comparing base (de247e5) to head (db3d40e).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #590      +/-   ##
==========================================
+ Coverage   86.65%   86.67%   +0.01%     
==========================================
  Files          16       16              
  Lines        2316     2319       +3     
==========================================
+ Hits         2007     2010       +3     
  Misses        309      309              

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[will-moore]

@jo-mueller - rebased and fixed tests