Allow multiple metrics with the same timing code.

`Genome::SoftwareResult::_faster_get` contains almost identical timing code to `Genome::Utilitiy:Instrumenttation::timing`. Unfortunately, in the current state it cannot be factored out because it uses the same timing information to record multiple metrics, which `timing` doesn't support.

This PR allows `Genome::Utilitiy:Instrumentation::timing` to take multiple metric names, while keeping the API the same for all current users.

Popping an item off `@_` doesn't seem particularly idiomatic to me, but I felt that preserving the current API (the coderef is the last argument) was more desirable in this case. Thoughts?