optimize flake shape and add devshell

lib/hosts.nix

@@ -0,0 +1,21 @@
+{ username }:
+{
+  darwin = {
+    name = "darwin";
+    kind = "darwin";
+    system = "aarch64-darwin";
+    hostname = "hari-macbook-pro";
+    homeModule = ../home;
+    homeDirectory = "/Users/${username}";
+  };
+
+  netty = {
+    name = "netty";
+    kind = "nixos";
+    system = "x86_64-linux";
+    hostname = "netty";
+    homeModule = ../home/netty.nix;
+    standaloneHomeModule = ../hosts/netty;
+    homeDirectory = "/home/${username}";
+  };
+}