See if we can use Arduino CLI for CI instead of PlatformIO

[FokkeZB]

• https://learn.adafruit.com/continuous-integration-arduino-and-you/testing-your-project
• https://github.com/arduino/Arduino/blob/master/build/shared/manpage.adoc

Upsides:

• Closer to the metal
• No (sometimes conflicting) platformio package manager intervening

Downsides:

• No linting

[FokkeZB]

• [x] Use Arduino CLI
• [x] Fix Messages/Send example
• [x] Install DHT library for sensor example