Less hacky offhand

[Lyfts]

WIP - better description might come later.
This is a bigger project that will attempt to make the offhand feel more like a true vanilla offhand. Allocates an actual inventory slot for the offhand and will also render a slot for it in the player inventory. Using an inventory slot for the offhand also enables us to completely remove all of the incredibly janky hotswaps and makes a lot more items usable in the offhand without having to add any special compat.

Huge amounts of duplicated vanilla code that had only small tweaks to allow for offhand has also been removed as we can just trick vanilla into doing the job for us.

Closes #44
Closes #41
Closes #28
Closes #39
Closes #33
Closes #37
Closes #43 (tested & works fine now)
Closes #32 (tested & works fine now)
#25 (tested & works fine now) Nevermind, they want to dual wield mana blasters and have them shoot alternatively. Not gonna be implemented in this pr.
Closes #36

Might also close the following but further testing is needed
#32
#20
#40 (this is almost certainly fixed, but I can't test it since the mod keeps crashing no matter what I try)

[Caedis]

This is looking to be an amazing rewrite

[Lyfts]

Alright, I think this is ready for review. There will almost certainly be bugs with a rewrite like this but overall I believe it leaves the mod in a much better, cleaner and functional state.

[Caedis]

creating a pre release to do some testing

[github-actions]

Warning: 2 uncommitted changes
pull request create failed: GraphQL: Head sha can't be blank, Base sha can't be blank, Head repository can't be blank, No commits between GTNewHorizons:unjankify and origin:GTNewHorizons-unjankify-spotless-fixes, Head ref must be a branch, not all refs are readable (createPullRequest)

[Caedis]

leaving open to let Lyfts merge if they think its good to go