Handle metrics of different lengths

[nnuss]

In many functions we have // TODO(...): make sure the arrays are all the same 'size'

And when it occurs (often because of resolution differences) we either have bad behavior, errors, or both.

Graphite appears to: find the least-common-multiple of the step size and munge the series to be the same 'size'

[Civil]

For graphite this is actually depends on render. So that's a subject to discuss how we should fix those TODO's. But they definitely should be fixed sooner or later.