ci: rework flake integration

Now Use flake part and integrate a build system using nix package building and treefmt-nix as a flake-part module

nix/treefmt.nix

@@ -0,0 +1,18 @@
+_: {
+  config.perSystem =
+    {
+      config,
+      inputs',
+      pkgs,
+      ...
+    }:
+    {
+      treefmt = {
+        programs = {
+          shfmt.enable = true;
+          alejandra.enable = true;
+          nixfmt.enable = true;
+        };
+      };
+    };
+}