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/build.nix

@@ -0,0 +1,34 @@
+{ inputs, ... }:
+let
+  inherit (inputs.flake-parts.lib) mkPerSystemOption;
+in
+{
+  options.perSystem = mkPerSystemOption (
+    {
+      pkgs,
+      config,
+      ...
+    }:
+    {
+      packages.default = pkgs.stdenvNoCC.mkDerivation {
+        name = "xiemeart";
+        src = ../.;
+        nativeBuildInputs = config.buildPackages;
+        configurePhase = ''
+          ln -snf ${config.pelicantheme} theme
+          ln -snf ${config.pelicanplugins} plugins
+        '';
+        buildPhase = ''
+          ls -la
+          mkdir -p output
+          pelican --verbose -o output/ 2>& 1>build.log
+        '';
+        installPhase = ''
+          mkdir -p $out/
+          cp build.log $out/
+          cp -r output/* $out/
+        '';
+      };
+    }
+  );
+}