Add simulation and unit tests

[SamCarlberg]

Remove direct hardware access from the subsystem and go through an IO layer. This is necessary so that we can simulate the robot's mechanisms on desktop and still use the same control configurations and setups (joystick inputs, path following, and commands).

Do the same for swerve modules - MAXSwerveModule hardware implementation becomes MAXSwerveModuleIO, with a corresponding IO object for use in simulation

Add a simple simulation framework to coordinate battery voltage droop from multiple mechanisms

Add some simple tests to demonstrate JUnit and test setup

See the documentation here on running simulation: https://docs.wpilib.org/en/stable/docs/software/wpilib-tools/robot-simulation/index.html

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I've attached three files to get started with the simulation GUI. Save these to your project folder before running simulation (for example, if you've cloned the repository to C:\Users\you\Documents\2023-swerve\, download these files directly into that folder). These are set up to show a simple field and robot UI, controllable with a keyboard. Use WASD to move and QE to rotate the robot. If the robot leaves the field, starting autonomous mode will reset its position to 0, 0 at the bottom left corner of the field.

simgui-ds.json
simgui-window.json
simgui.json