Add Arduino CI

[2bndy5]

This adds a CI workflow to compile the examples against AVR and SAMD cores. Also I formatted the examples using AStyle formater (as used in the Arduino IDE). Additionally, I replaced the direct calls to printf() with Serial.print*() (its likely I missed some) in the examples. This also closes #165 by removing the sync.* files per recommendation of @TMRh20

Exceptions

I had to skip checking a couple examples:

1. Network_Ping
   • The Arduino CLI doesn't seem to have "avr/pgmspace.h" included
2. Network_Ping_Sleep
   • had trouble with this one because the RF24Network::sleepNode() & RF24Network::setup_watchdog() aren't defined for all cores, even though this example does compile for AVR cores (not SAMD core).

Also, I didn't add the SpenceKonde ATTinyCore for now. I thought it might be better to work out which platforms/cores would work for the above examples.

About doing a Linux Build CI

My attempts to add a linux build workflow were rather fruitless (see commit titles). The error that I couldn't work out is

/usr/bin/ld: skipping incompatible //usr/local/lib/librf24-bcm.so when searching for -lrf24-bcm
/usr/bin/ld: cannot find -lrf24-bcm

when executing file /usr/local/lib/librf24.so.1.3.11 (because librf24-bcm.so is just a symlink to librf24.so.<latest>), I get the following:

usr/local/lib/librf24.so.1.3.11: ELF 32-bit LSB shared object, ARM, EABI5 version 1 (SYSV), dynamically linked, BuildID[sha1]=b962e32a88f2d4e188c85011c107b2c1b9579a3d, with debug_info, not stripped

the output from the same cmd on my RPi4 is

/usr/local/lib/librf24.so.1.3.11: ELF 32-bit LSB pie executable, ARM, EABI5 version 1 (SYSV), dynamically linked, BuildID[sha1]=ce6b682fd3d68c07820a177d7f5bba01b3e4ea6b, with debug_info, not stripped

Notice the "LSB shared object" vs "LSB pie executable"