cellpheno/nis: add test tile + models

[Chrisa142857]

Test data for the cellpheno/nis module (nf-core/modules#12179).

• data/imaging/segmentation/cellpheno_nis/cellpheno_nis_tile.zip — a real P4 partial-brain crop: 30 z-slices, 384×384 (2D OME-TIFF), ~4 MB.
• data/imaging/segmentation/cellpheno_nis/cellpheno_nis_models.zip — the TorchScript NIS models (cuda:0 set), ~64 MB.

Both are zipped so the module test extracts them via the UNZIP subworkflow (dir inputs), following the numorph/3dunet pattern. Verified: NIS segments 351 nuclei on this crop.

[mashehu]

this file is too big, we usually aim for as small as possible, target <1MB. Any chance you can shrink this and the second file?

[Chrisa142857]

Thanks @mashehu! Addressed:

• Shrank the tile to a smaller real P4 crop (16 slices, 224×224) — now ~700 KB (<1 MB).
• Dropped the models zip entirely: the TorchScript weights (~64 MB) are large and available via gdown from the source G-drive, so they don't belong in test-datasets — the module test fetches them at runtime instead of bundling them here.

So this PR now adds a single ~700 KB file. NIS still segments 221 nuclei on the crop.

[mashehu]

awesome and thanks for cleaning up the git history!