flatten and sort all flake inputs

flake.nix

 {
   inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs?ref=nixos-unstable";
+    attic.url = "github:zhaofengli/attic?ref=main";
+    crane = { url = "github:ipetkov/crane?ref=master"; inputs.nixpkgs.follows = "nixpkgs"; };
+    fenix = { url = "github:nix-community/fenix"; inputs.nixpkgs.follows = "nixpkgs"; };
+    flake-compat = { url = "github:edolstra/flake-compat"; flake = false; };
     flake-utils.url = "github:numtide/flake-utils";
     nix-filter.url = "github:numtide/nix-filter";
-    flake-compat = {
-      url = "github:edolstra/flake-compat";
-      flake = false;
-    };
-
-    fenix = {
-      url = "github:nix-community/fenix";
-      inputs.nixpkgs.follows = "nixpkgs";
-    };
-    crane = {
-      url = "github:ipetkov/crane?ref=master";
-      inputs.nixpkgs.follows = "nixpkgs";
-    };
-    attic.url = "github:zhaofengli/attic?ref=main";
+    nixpkgs.url = "github:NixOS/nixpkgs?ref=nixos-unstable";
   };
 
   outputs =