Fan control for MacBook/MacMini, spiritual successor to macfanctld.

This is a software to control the Macbook, MacbookPro, and MacMini machine's SMC interface to obtain temperature sensor reaings and use it to control the system's fan on the same interface.

When running Linux on the Mac devices, the SMC is used to read the temperature sensors and control the fan. The driver does not have the bindings between the two that allows lm_sensors to control the fan. Therefore a separate program will be needed to manage the fans.

Additional requirement too, may arise from needing to define custom group of sensor -> fan control. This can be because one might want to turn on the fan when the GPU is in use more, to prevent throttling. Or to give battery or harddrive more cooling based on detected temperature in those sensor readings.

• Uses a layered, tiered sensor groups to control the fans that is essentially the same as macfanctld.
• Switched to using Modern C++ (C++20)
  • There was a lot of bugs: integer sanity, address sanity, memory management issues that is simply solved by using STL, instead of writing from scratch or finding more dependency libraries.
  • The entirety of the program logic: config parser, control loop, SMC interface now fits in <500 lines of code comfortably.
• Switched to using json for configuration file
  • Removed having to write a config file parser and allows any number of groups instead of the traditional fixed groups.

• No Unit Tests yet, but -Werror -Wall -Weverything as default compile flag. Yes this means compile with clang...
• Allows user to define their own custom groups of sensors and use that to drive the sensors in a porportional controller for the fan. This is one of the original reason I decided to use macfanctld over the other programs (despite not having UTs, and possible bugs, etc.)
• Configuration file that is not in obscure, hard-to-read format that is clunky.

• Been using it as daily driver for MacbookPro14,2 for a while doing development work (many Firefox tabs, light compiles, streaming, OBS, gstreamer encode/decode, youtube, Google Meet/Chat, etc.)
• Recented started using it on my MacMini6,2 also (mainly a media/gaming machine)

• Handling signals, daemonize?
• Unit tests, code clean up, break up into files instead of one huge file.
• Switch to single thread async model: epoll(), libuv, libev type of system (instead of round-robin file polling)
• Manual overrides: TBD interaction
• Not a full PID controller
  • Only has a porportional factor (see doc for more algorithm detail)
  • This means the controls can swing more, might be noisier. (I and D parts)
• No shut offs either, so the fan might be running more than on it is on MacOS (I'm trading for lower temp here) But it stands to reason that a hysteresis shutoff might be good to have to prolong the life of the fans (esp. on the older Macs).
• GUI, display, status report, notification
• DBus
• Proper logging
• A generic, global group actions; more actions and sensor process methods.

• Possibly running this with my Raspberry Pi 4 case (it uses a percentage system also). What a strange idea. Maybe. We'll see.

• clang, recent version that supports std::filesystem
• nlohmann::json, it makes json so easy.

• Kernel that supports the SMC and a Mac machine.