Improved vector tests; removed redundant benchmarks

[regexident]

Vector's operations shallowly wrap those from "Arithmetic", so there's really no point in benchmarking them, when we already have benchmarks in place for the latter.

Vector tests now also moved from explicit expected values via literals to ad-hoc un-optimized calculations of the operation.

[mattt]

Nice! I especially like the change from literals to constructors.

Only thing I bumped on was the use of explicit Swift. namespacing for the zip function (and maybe also Surge.dist). Are these necessary to satisfy compiler type checking, or stylistic (apologies if I'm missing an obvious collision somewhere).

[regexident]

Swift.: I prefer to stay on the safe side of things, given Swift's lack of coherence/orphan checks, hence I got used to adding Swift. whenever I use a top-level function from the stlib.

I removed them in c86b964. :)

[mattt]

@regexident I definitely get where you're coming from — I remember getting bitten by that in early versions of Swift (IIRC in relation to Darwin functions). But I think you made the right choice with 53b46a6; an explicit but unnecessary Swift. could cause an observer to think that the current module (or an imported one) defines a function with the same name. So thanks for that!