use separate encoding for temporary subchunkables #1088
Description
Subchunkable will use the same encoding for temp paths as the final output layer, which can be a problem for two reasons:
- lossy compression artifacts accumulate
- some image formats don't support the large chunks we use in temporary layers (e.g. max JPEG size is 65k x 65k px)
Need a way to overwrite the encoding for subchunkable intermediary layers