hoists cell support to /obj/item/gun, adds in partial modular guncrafting API

[silicons]

the issues with guncrafting is generally like

• inefficient (like 5-6 items per gun)
• bad UX (needing to slot 5 things into the gun, no one wants to print out "this is just a stock energy lens lol")
• implementation is horrible (good luck having it on more than one type)

solution:

attachment-like system where the default is a usable gun and everything is efficient
functionality are done via mostly signal intercepts and event structs, with very few snowflake APIs (particle arrays will need one later on.)