Remove singleton dimensions in compute_to_zarr

[felixcremer]

We remove singleton dimensions which we might had to include to allow the DiskArrayEngine algorithm to track them before saving the data to zarr.

We have to remove these singleton dimensions because zarr can't have the same dimensions in a group with different length.

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 69.74%. Comparing base (3a9f5d7) to head (c84a756).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/DAT/xmap.jl	83.33%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #610      +/-   ##
==========================================
+ Coverage   69.66%   69.74%   +0.08%     
==========================================
  Files          15       15              
  Lines        2212     2228      +16     
==========================================
+ Hits         1541     1554      +13     
- Misses        671      674       +3     

Files with missing lines	Coverage Δ
src/DAT/xmap.jl	56.10% <83.33%> (+1.40%)	⬆️

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[lazarusA]

let's merge and patch release this, although it will be nice to have a look from @meggart