chore: move packages out of source

[sleepdefic1t]

Summary

External libraries are currently submoduled in the source tree which leads to more complex builds and makes maintaining and debugging more difficult.

This PR moves external libraries to extern in the root dir and drops submodules in favor CMake methods of fetching dependencies.

Specifically, this PR does the following:

• removes all git submodules.
• adds CMake configs to get extern libs.
• updates CMake configurations and naming.
• makes building tests optional.
• updates build scripts.
• updates Actions/CI scripts and workflow.
• updates PIO configuration files.
• updates the Arduino IDE helper script.
• updates the changelog.

Checklist

• Documentation (if necessary)
• Tests (if necessary)
• Ready to be merged

Additional Comments

PIO build failure is resolved in #139

[faustbrian]

@sleepdefic1t platformio failing