Improve USB to Serial/JTAG TX
Improve USB to Serial/JTAG TX

It had a tight 5ms timeout before that caused some characters to
drop. Now the wait is longer and reset after a successful transmit.
This follows what MicroPython does.

Fixes #6220

adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython,adafruit/circuitpython