over-use of cloning on things that could be dereferenced or simply passed by reference

[robfitzgerald]

noting that

• there are quite a few places where something like a newtype is being cloned just because the function signature expects a type passed by value, not by reference (see the units libraries like Distance and DistanceUnit, etc)
• some things are being passed by value that could be passed by reference, and those calls end up cloning those values (can't think of where i've seen this but i know there's a good deal of it)

this unnecessary cloning adds a time and space complexity hit when we are talking about low-level operations such as unit conversion, serialization, or anything in the loop of search, so we should go spelunking to remove them.