Quite extensive refactor of Telemetry

- just store the nqp::getrusage struct instead of already dissecting
  - makes Telemetry.new about 15% faster
  - adapt all instance method logic accordingly
  - moves burden to Telemetry::Period creation, but that's when we need
    and all of the snapping is already done
- store wallclock internall as nqp::time_n value, without conversion
  - makes Telemetry new about 5% faster
  - outside API is still microseconds
  - adapt all calculations depending on wallclock accordingly
- use arrays of names of rusage struct and scheduler info
  - instead of writing it all out
- remove "ics" from the default report
  - not sure what info it really gives anyway
- make proto's use {*} as per new guidelines
- makes source-file about 20% smaller, hopefully aiding in maintainability