Fix thread index values

[jrmadsen]

• ensure that all background threads via PTL and perfetto are not accidentally indexed as user threads
  • PTL submodule waits for threads to start before proceeding
  • Initialize perfetto after pthread_create wrapper activated
• tweak to backtrace component
  • exclude gotcha call-tree
• tweak to callchain component
  • callchain::get sorts based on timestamp
  • callchain::sample supports duplicate IPs (e.g. recursion)