bug in 3d running

Merge pull request #1472 from MouseLand/slice_3d_labels

Slice 3d labels

Merge pull request #1470 from MouseLand/doc_fix

update doc string #1469 and import error message

Merge pull request #1423 from MouseLand/saturation_fix

Gray saturation fix: drop blank channels from mean

Merge pull request #1417 from MouseLand/refactor_eval

Refactor eval

Merge pull request #1406 from tlambert03/fix-nd2

fix nd2 reading on drop event

explicitly fail loading cp4 model in cp3

Merge pull request #1374 from MouseLand/batch_img_refactor

Batch img refactor

Merge pull request #1341 from MouseLand/faq_update

Faq update

Merge pull request #1260 from MouseLand/add_back_cp3_nb

add notebook for running cellpose3 with denoising and segmentation