Audit public API to take arguments by reference where possible before v1.0 release

[spacebear21]

Don't consume values unless there is a reason for doing so. Make sure that arguments which take ownership of a value do so intentionally.

Search for .clone() in integration tests...

[benalleng]

I will try my hand at this, a lot of these issues look like they are some good practice on rust fundamentals on when and where to use references, Copy traits and whatnot

[DanGould]

@benalleng please pick up from #405 if you're up for it. Lots of small PRs will let us crank forward progress on this one. I'm not tied to getting #405 in myself, it was really a way for us to enumerate problems where we saw them when we were in person

[bc1cindy]

Hey @DanGould @spacebear21 I'd like to work on this issue