refactor(flake)!: export packages using a flake module

Also stop passing `outputs` around, prefer `inputs.self`
Also put all `auto_` in `readOnly` `internal` options
- `autoModules`, `autoConfigurations` and `autoPackages`
Do not export packages as overlay (causes an infinite recursion)
- this is documented on the two places it has effect on
-- in `./overlays/default.nix` and `./modules/flake/configurations.nix`
-- in `autoConfigurations` we manually extend `pkgs` with the flake packages
Allow packages to say what `systems` they are compatible with
- See `./pkgs/swww/systems.nix` - disabled for all systems
- See `./pkgs/pngpaste/systems.nix` - enabled only for `darwin` targets

nix/utils.nix

@@ -1,4 +1,4 @@
-{ lib, self, ... }:
+{ lib, config, self, ... }:
 
 rec {
   # Boolean helpers
@@ -109,10 +109,7 @@ rec {
       (lib.genAttrs
         configuration-types
         (configuration-type:
-          let
-            hosts = configuration-type-to-outputs-hosts configuration-type;
-          in
-            self.${hosts}))
+          config.flake.autoConfigurations.${configuration-type}.resultHosts))
       (configuration-type: hosts:
         lib.pipe
           hosts