Split export to multiple OBJs + padding for optimization

[StandingPadAnimations]

A common technique to reduce performance issues from large exports is to slice it up into multiple OBJs, and assemble them in 3D software separately. Currently, this has to be done manually, so it would be nice if we could have a sort of "split to multiple files" option, that simply splits the export to multiple files based on a pre-defined chunk size. Essentially, taking one selection, and turning it into multiple selections and exporting them individually

The only thing this would require that is not yet implemented is a way for jmc2OBJ to consider blocks outside of the selection when optimizing the mesh. Even when manually exporting chunks, unless render world sides is enabled (which adds a lot of geometry), the final assembly of OBJs may contain holes at the boundaries between 2 pieces (attached below is an example). While this can be mitigated with enabling world sides, as noted earlier, this adds a lot of additional geometry that ends up being unnecessary (especially in the "interior" of the assembly).

A way to avoid this would be to have a "padding" value (maybe 1 block by default) that simply extends the sides of the bounding box by $n$ amount of blocks, with the extended bounding box being used when deciding what faces to remove (but the original bounding box still being used for exports).