feat: use flake-parts and auto-generate nixosConfigurations for all hosts

hosts/default.nix

@@ -0,0 +1,20 @@
+{inputs, self, ...}:
+let
+  inherit (inputs.nixpkgs) lib;
+  isDirectory = _name: type: type == "directory";
+  hostNames = builtins.attrNames (
+    lib.filterAttrs isDirectory (builtins.readDir ./.)
+  );
+  hosts = lib.genAttrs hostNames (name: {
+    modules = [
+      (./. + "/${name}")
+    ];
+  });
+in 
+{
+  flake.nixosConfigurations = lib.mapAttrs (host: hostConfig: lib.nixosSystem {
+    inherit (hostConfig) modules;
+    system = "x86_64-linux";
+    specialArgs = { inherit inputs; };
+  }) hosts;
+}