I had some time free, and noticed how awful the reagent grinder code was - it used huge static lists containing types and their associated reagents from grinding.
This is now split into two new vars on /obj/item - var/list/grind_results and var/list/juice_results, as well as two new helper procs, on_grind() and on_juice() to allow those to change based on conditions like plant potency. Such checks and the like have been moved to that. If any of these procs return -1, the operation is canceled.
I also fixed some of the recipes that didn't work. The reagent IDs for them didn't exist, leading me to believe that they weren't tested. I corrected that! (I've tested every single recipe in this PR, with the exception of a few juicing-related ones.)
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