refactor: format nix code with alejandra & rename nix files for clarity

nix/default.nix

@@ -1,78 +0,0 @@
-{
-  lib,
-  libX11,
-  libinput,
-  libxcb,
-  libxkbcommon,
-  pcre2,
-  cjson,
-  pixman,
-  pkg-config,
-  stdenv,
-  wayland,
-  wayland-protocols,
-  wayland-scanner,
-  libxcb-wm,
-  xwayland,
-  meson,
-  ninja,
-  scenefx,
-  wlroots_0_19,
-  libGL,
-  enableXWayland ? true,
-  debug ? false,
-}:
-stdenv.mkDerivation {
-  pname = "mango";
-  version = "nightly";
-
-  src = builtins.path {
-    path = ../.;
-    name = "source";
-  };
-
-  mesonFlags = [
-    (lib.mesonEnable "xwayland" enableXWayland)
-    (lib.mesonBool "asan" debug)
-  ];
-
-  nativeBuildInputs = [
-    meson
-    ninja
-    pkg-config
-    wayland-scanner
-  ];
-
-  buildInputs =
-    [
-      libinput
-      libxcb
-      libxkbcommon
-      pcre2
-      cjson
-      pixman
-      wayland
-      wayland-protocols
-      wlroots_0_19
-      scenefx
-      libGL
-    ]
-    ++ lib.optionals enableXWayland [
-      libX11
-      libxcb-wm
-      xwayland
-    ];
-
-  passthru = {
-    providedSessions = ["mango"];
-  };
-
-  meta = {
-    mainProgram = "mango";
-    description = "Practical and Powerful wayland compositor (dwm but wayland)";
-    homepage = "https://github.com/mangowm/mango";
-    license = lib.licenses.gpl3Plus;
-    maintainers = [];
-    platforms = lib.platforms.unix;
-  };
-}