modifies the hollow metrics API; that'll probably be implemented soon
adds init stages
changes SSatoms to not abuse its `initialized` variable
closes#6858
i decided i'm following in stylemistake's light
the files in this pr are entirely written by me instead of regurgitated
tgcode;
i'm also marking a lot of other files but they're in their own prs
(inventory module in hand pr, materials/atom damage related stuff in
atom damage, etc)
Co-authored-by: silicons <no@you.cat>