Added superclass for instance segmentation models and modified ilastik object classification to inherit from it

Added superclass for semantic segmentation models and modified ilastik pixel classification to inherit from it

Delegated export of patch products to ZMaskObjectTable class; consolidated both batch runner and API-facing workflows into infer_object_map_from_zstack(); consolidated parameterization of export products into pydantic model

Validated non-duplication when loading ilastik model with same project file name, irrespective of path formatting

Made the one implemented ilastik object classification model accomodate only the ilastik workflow that requires pixel prediction maps

Start online validation of autogenerated model; but need to make inference model that takes binary inputs

Pass notebook filename and not path to load an ilastik model; assumes project files are in conf.server.paths['ilastik']

(1) slicing to a single-channel image now returns its own accessor object; (2) channel slicing now happened at image accessor level, i.e. model is agnostic; (3) TIFF export is now a utility method, not a subclass of accessor