Write best practice for stacking arrays (and benchmark!)

[jlperla]

A classic example is stacking up various vectors/values in a single vector for a solver.

• An approach is to use the ArrayPartition in https://github.com/JuliaDiffEq/RecursiveArrayTools.jl
  • Sounds like it has some slowdowns with indexing.
• Another is https://github.com/ahwillia/CatViews.jl splitview which cleanly deconstructs the vector into - different views, but where the views themselves are probably set as constants
• Finally, we could just keep constants for the indexes and just use views and/or subarray indexing?