Fix boundary issues for ome-zarr writing

[K-Meech]

• fixes OME Zarr chunking mobie-viewer-fiji#572 (This was an error with the reading during the 'loopBack' here: https://github.com/mobie/mobie-io/blob/develop/src/main/java/org/embl/mobie/io/n5/util/ExportScalePyramid.java#L152 for accessing previously written levels (but only when writing very downsampled levels).
• added some simple tests for writing images in different formats + checking they can be read
• updated junit dependencies + added dependency for newer spim_data (this is needed for the writing tests to run properly)
• removed serialisation of nulls when writing ome-zarr metadata. This prevents e.g. null transformation parameters being written.

[K-Meech]

The tests fail here, but this is just because I updated the junit dependency: #54. These tests already fail on the current develop branch.

[KateMoreva]

Thank you for your work!
I think it is better to merge it.

I'll fix the failing tests after that.