Nano ESP32: allow `machine.bootloader` to run either hardware or DFU bootloader

[pillo79]

Summary

The machine.bootloderimplementation on the Arduino Nano ESP32 is different from other Espressif-based boards in that it calls a custom "bootloader" (actually, a different application) which allows DFU uploads. This allows users to easily switch between Micropython and Arduino C environments.

However in some cases the hardware bootloader is still useful - for example when a full flash is required. This PR introduces argument parsing of the machine.bootloader() implementation so that when it is called with 1 as argument, the hardware bootloader is started - in all other cases, as before, the Arduino bootloader will run.

Testing

Tested on Arduino Nano ESP32:

• machine.bootloader() starts the Arduino bootloader (for use with dfu-tool)
• machine.bootloader(1) starts the ESP32-S3 hardware bootloader (for use with esptool)

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.43%. Comparing base (6c3dc0c) to head (b3b99ab).

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #15697   +/-   ##
=======================================
  Coverage   98.43%   98.43%           
=======================================
  Files         163      163           
  Lines       21290    21290           
=======================================
  Hits        20956    20956           
  Misses        334      334           

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[github-actions[bot]]

Code size report:

   bare-arm:    +0 +0.000% 
minimal x86:    +0 +0.000% 
   unix x64:    +0 +0.000% standard
      stm32:    +0 +0.000% PYBV10
     mimxrt:    +0 +0.000% TEENSY40
        rp2:   +16 +0.002% RPI_PICO_W
       samd:    +4 +0.002% ADAFRUIT_ITSYBITSY_M4_EXPRESS

[dpgeorge]

Thanks for the contribution. This will need to wait until #15108 is merged.

[pillo79]

@dpgeorge Rebased to include the now-merged #15108.