[Suggestion] Generify "items" travelling through pipes for addon purposes

[Quarris]

please it make addons ez mode

[Ellpeck]

Note to self: My current idea is to expand the TYPES registry to PipeItemType, which allows constructing and loading PipeItem instances like now, but also allows adding additional capabilities, checks, and abilities to pipes and pipe networks by iterating each registered pipe item type when checking for abilities. I'd also like to get rid of IPipeItem and turn PipeItem into an abstract class that shares all important values like position, path compiling, and start and goal inventory caches.