feat: add debug sensor for development workflow on hardware that does…

[sfishel18]

…n't support any existing sensors

[sfishel18]

👋 hello! i came across your product searching for open source projects working to fight climate change. i'd love to contribute if i can.

the first challenge i had trying out the code base was that i don't have easy access to bare-metal Linux. i do development on a Mac and generally deploy things on GCP. so i had the thought to get some experience with the code by introducing a "debug" sensor that would just output synthetic power consumption information without requiring the underlying hardware to be compatible with the powercap/rapl sensor.

it's turning into a larger refactor than i intended, so i thought it would be best to pause where it is and put it up for discussion:

• is this functionality generally useful to more than just me?
• is this the right approach to adding it?

also, i'm new to Rust, so any feedback on code style and patterns is very welcome!