Add Nix flake and improve derivation

This adds a Nix flake to the repo as well as updates the derivation so
that it includes `lzip` as a dependency

default.nix

@@ -1,22 +1,4 @@
-with (import <nixpkgs> {});
-
-stdenv.mkDerivation {
-  name = "waydroid_script";
-
-  buildInputs = [
-    (python3.withPackages(ps: with ps; [ tqdm requests inquirerpy ]))
-  ];
-
-  src = ./.;
-
-  postPatch = ''
-    patchShebangs main.py
-  '';
-
-  installPhase = ''
-    mkdir -p $out/libexec
-    cp -r . $out/libexec/waydroid_script
-    mkdir -p $out/bin
-    ln -s $out/libexec/waydroid_script/main.py $out/bin/waydroid_script
-  '';
-}
+let
+  pkgs = import <nixpkgs> {};
+in
+  pkgs.callPackage ./package.nix { }