add a low-lag get_by_id

because the isClient check is slow, and some classes only exist server
side, so know which side they are on.
and use the unsafe get

assuming the code will only be used server side.
quickset for when the manual lock is alrady set

and you don't mind a very small chance that the thread won't release.
also, do more inventory udpates per tick; noticed a bit of pipe HUD lag
on the send queue.