…ns; convert API to slice

There was never any need for this function to take in a &Vec; we should never do that. Instead take in a slice.

Additionally, we refactored some of the loop logic to use .take instead of a check on each iteration to see if we were at the end. We also combined two duplicate for loops into 1.

Finally, we significantly refactor the return type to avoid a lot of very expensive cloning. Previously, we were doing something on the magnitude of 9 clones (of expensive underlying objects including vectors) per input GroveDbOp. All of these have been removed. We instead return references to these values instead of clones of them. This does mean that the lifetime of the return value is tied to the underlying data the slice refers to; but especially as I cannot even find an instance where we use these return values, this feels like a very fair trade off.