GitHub actions: embedded targets

[malachib]

Add ESP-IDF and RPI Pico targets to build Unity tests

Consider using:

1. https://github.com/marketplace/actions/pico-build-action
2. https://github.com/espressif/esp-idf-ci-action

Ideally targeting stable and beta ESP-IDF
Also last I checked RPI Pico compiled well without a lot of extra, so perhaps regular cmake action is sufficient?

Bonus: consider QEMU or similar to run things

[malachib]

https://github.com/marketplace/actions/esp32-qemu-runner

NOTE: Unclear if we can practically capture & measure test results from QEMU