Add joystick support

[cboulay]

Library	Cross-Platform	Headless	Status	Notes
https://pysdl2.readthedocs.io/	Yes	Yes	Active	Can init only joystick/controller subsystems without video
https://github.com/zeth/inputs	Yes	Yes	Unmaintained (2019)	Reported issues on macOS
https://pyglet.readthedocs.io/en/latest/programming_guide/input.html	Yes	No	Active	Requires event loop + window
https://www.pygame.org/docs/ref/joystick.html	Yes	No	Active	Requires SDL video init
https://python-evdev.readthedocs.io/en/latest/	Linux only	Yes	Active	Very clean API

For headless ezmsg integration, PySDL2 seems best because:

• Can run without a window: sdl2.SDL_Init(sdl2.SDL_INIT_GAMECONTROLLER)
• Cross-platform (Windows, macOS, Linux)
• Uses battle-tested SDL2 under the hood
• See Discussion: sdl2.ext2.joystick? py-sdl/py-sdl2#171 for an example Joystick implementation

Additional info:

• https://courses.ideate.cmu.edu/16-375/f2025/text/python/gamepad.html
• https://wiki.libsdl.org/SDL3/CategoryGamepad