Because there is no option to create a `remapped-mojang` artifact for 1.16.5 and the whole point of the scripts is to save me time, 1.16.5 support is being removed earlier than usual.
Also fixes issues with NMS-based shulker collision check.
Closes#36
* Reduce duplicate code
* Use more specific functional interfaces where available
* Fix some potential NPEs
* Remove some unnecessary/nonfunctional code
* Merge inventory listeners - no longer need to keep separate due to event availability
* Removed TODO items that probably won't ever be implemented. Good ideas, too drastic changes or too much work to maintain.
