pw_sys_io_arduino: Wait up to 3s before starting serial on Teensy
pw_sys_io_arduino: Wait up to 3s before starting serial on Teensy

This gives the host machine time to connect to the Teensy so startup
serial output isn't missed.

Change-Id: I5df298918601a77bd2e951f8fdc015d4fd080481
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/43223
Pigweed-Auto-Submit: Marc MERLIN <7073d0fab1ea36cd0c0f1f603a2a5e44b931b31c@google.com>
Commit-Queue: Anthony DiGirolamo <4cc40125edc24ec5bc72df7917ea0b403ee8cebe@google.com>
Reviewed-by: Armando Montanez <97ef6fdb231c129ac8827d9f0c4106bfbf57f74f@google.com>

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed