Support more itk types

Currently the imagej-itk bridge converts all images to 32 bit float and returns 32 bit float. We need to update the converters to support other types.

Start by locating the imagej-itk image converter entry points and tracing where images are forced to 32-bit float. Determine which additional image types the bridge must preserve, then verify that conversion and return paths handle those types without reducing them to 32-bit float.

Written by the indexing model from the issue text.