Fixed rollback

[forman]

Fixed rollback for situations where writing to Zarr fails shortly after the Zarr directory has been created.

Closes #69

Checklist (strike out non-applicable):

• [x] Changes documented in CHANGES.md
• [x] Related issue exists and is referred to in the PR description and CHANGES.md
• [ ] ~Added docstrings and API docs for any new/modified user-facing classes and functions~
• [ ] ~Changes/features documented in docs/*~
• [x] Unit-tests adapted/added for changes/features
• [x] Test coverage remains or increases (target 100%)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 99.85%. Comparing base (b75706a) to head (9b5bfa7).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #70 +/- ## ======================================= Coverage 99.85% 99.85% ======================================= Files 26 26 Lines 1371 1372 +1 ======================================= + Hits 1369 1370 +1 Misses 2 2 ```

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[forman]

Thanks @thomasstorm!