TST: a compile-test loop that activates -O2, increasing performance by >10x; TST: test 10x more iterations
ENH: add modal switches (still need to look up how to index into this vec); DOC: discuss our choice of an acyclic digraph graph topology for profiles but a simple tree for devices; REF: reorder various structs and enums
REF: Move profile-related code into its own file, out of device.rs.