Revamp all templates to remove flake-utils and nixpkgs-unstable

clojure/flake.nix

@@ -3,13 +3,10 @@
 
   inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
 
-  outputs =
-    { self
-    , nixpkgs
-    }:
+  outputs = { self, nixpkgs }:
 
     let
-      javaVersion = 17;
+      javaVersion = 20;
       overlays = [
         (final: prev: rec {
           jdk = prev."jdk${toString javaVersion}";
@@ -22,7 +19,8 @@
       forEachSupportedSystem = f: nixpkgs.lib.genAttrs supportedSystems (system: f {
         pkgs = import nixpkgs { inherit overlays system; };
       });
-    in {
+    in
+    {
       devShells = forEachSupportedSystem ({ pkgs }: {
         default = pkgs.mkShell {
           packages = with pkgs; [ boot clojure leiningen ];