fix: don't rely on std.time.microTimestamp() for accurate statistics

[robbielyman]

I don't know the extent to which you care about accuracy for rendering statistics. I found when working on seamstress that the timestamp calls in std.time were so unreliable as to be unusable, sometimes reporting negative time deltas within a single
function. std.time.Timer, on the other hand, has been rock-solid in my experience.

[rockorager]

Thanks! The stats don't need crazy accuracy, but I'll always take more accuracy if it doesn't cost much!