add nixbased build ci

.gitea/workflows/nix-check.yaml

@@ -0,0 +1,13 @@
+name: Verify build
+run-name: ${{ gitea.actor }} is building
+on: [push]
+
+jobs:
+  verify_build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: cachix/install-nix-action@v30
+        with:
+          nix_path: nixpkgs=channel:nixos-24.11
+          - run: nix-build

.gitignore

@@ -1,3 +1,4 @@
 /a.out
 /.zig-cache/
 /zig-out/
+/result

default.nix

@@ -0,0 +1,33 @@
+# default.nix
+{ pkgs ? import <nixpkgs> {} }:
+
+pkgs.stdenv.mkDerivation {
+  pname = "RatChess";
+  version = "0.0.1";
+
+  src = ./.;
+
+  nativeBuildInputs = with pkgs; [
+    zig
+    zls
+  ];
+
+  buildInputs = with pkgs; [
+  ];
+
+  buildPhase = ''
+    echo "Building project..."
+    ${pkgs.zig}/bin/zig build --global-cache-dir ./cache  --release=fast
+  '';
+
+  installPhase = ''
+    mkdir $out
+    cp -r zig-out/* $out/
+  '';
+
+  checkPhase = ''
+    echo "Testing project..."
+    ${pkgs.zig}/bin/zig build test --global-cache-dir ./cache
+  '';
+  doCheck = true;
+}