build: add nix flake

Author: Kiyotoko

flake.nix

@@ -0,0 +1,33 @@
+{
+  description = "seekers-api";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-25.05";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs =
+    {
+      nixpkgs,
+      flake-utils,
+      ...
+    }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = import nixpkgs {
+          inherit system;
+        };
+        stdenv = pkgs.stdenv;
+        lib = import nixpkgs.lib;
+        shell = nixpkgs.legacyPackages."${system}".callPackage ./shell.nix {
+          pkgs = pkgs;
+          lib = lib;
+        };
+      in
+      {
+        # enables use of `nix shell`
+        devShell = shell;
+      }
+    );
+}

shell.nix

@@ -0,0 +1,17 @@
+{
+  pkgs ? import <nixpkgs> { },
+  lib ? import <nixpkgs/lib> { },
+  ...
+}:
+
+pkgs.mkShell {
+  packages = with pkgs; [
+    nixfmt-rfc-style
+  ];
+
+  nativeBuildInputs = with pkgs; [
+    python312Packages.pygame
+    python312Packages.grpcio
+    python312Packages.protobuf
+  ];
+}