Measures dev-tree launches against a throwaway profile, without changing
main.js: time to app ready, toolbar and first page; main-thread blocks; add-on
activation; overlay pages loaded; main-process fetches; process count and
private memory at 15 s. One row per run, so a startup change can be compared
with the numbers before it.
node scripts/boot-trace/run.mjs [--runs 3] [--seconds 25] [--fresh] [--profile <dir>]
