Core: Add a test suite

[vaxerski]

Currently we only test whether hyprland compiles, but we don't actually test... well, anything else.

This MR is a WIP that adds a test suite.

For now it runs, works, and tests spawing two kitties with smart gaps, that's about it.

TODOs:

• Test... well, more.
• Add a plugin that will be built alongside to allow for simulating keystrokes mouse strokes and other stuff
• consider thinking about visual tests?

@fufexan nix, meson, ci pls? Tester needs to be ran from /hyprtester, btw.

cc @PaideiaDilemma @gulafaran

[fufexan]

Good idea, but I suggest we use https://nix.dev/tutorials/nixos/integration-testing-using-virtual-machines.html. These are much simpler to use since we don't need to build our own testing framework, and there are plenty of examples to help.

I'll try to cook something up today or tomorrow if I have time.

[vaxerski]

what? Just run the tester and fail if it returns non-zero