Add Nix (#177)

* add Nix support

* fix formatter output

* mention Nix in README

* fix common import

* fix frontend old version import

* clarified flake pkgs order

* rm old dataDir option

* comment typo

* fix password assertion

* rm old User/Group logic

* rewrite assertion boolean expr

* General flake touchup

- Rewrite `callPackage` exprs to be more readable
- Add pre-commit support for devShell
- Add direnv support

* add simple test

* use correct test func

nix/server.nix

@@ -0,0 +1,52 @@
+{ yt-dlp-web-ui-frontend, buildGoModule, lib, makeWrapper, yt-dlp, ... }:
+let
+  fs = lib.fileset;
+  common = import ./common.nix { inherit lib; };
+in
+buildGoModule {
+  pname = "yt-dlp-web-ui";
+  inherit (common) version;
+  src = fs.toSource rec {
+    root = ../.;
+    fileset = fs.difference root (fs.unions [
+      ### LIST OF FILES TO IGNORE ###
+      # frontend (this is included by the frontend.nix drv instead)
+      ../frontend
+      # documentation
+      ../examples
+      # docker
+      ../Dockerfile
+      ../docker-compose.yml
+      # nix
+      ./devShell.nix
+      ../.envrc
+      ./tests
+      # make
+      ../Makefile # this derivation does not use the project Makefile
+      # repo commons
+      ../.github
+      ../README.md
+      ../LICENSE.md
+      ../.gitignore
+      ../.vscode
+    ]);
+  };
+
+  # https://github.com/golang/go/issues/44507
+  preBuild = ''
+    cp -r ${yt-dlp-web-ui-frontend} frontend
+  '';
+
+  nativeBuildInputs = [ makeWrapper ];
+
+  postInstall = ''
+    wrapProgram $out/bin/yt-dlp-web-ui \
+      --prefix PATH : ${lib.makeBinPath [ yt-dlp ]}
+  '';
+
+  vendorHash = "sha256-guM/U9DROJMx2ctPKBQis1YRhaf6fKvvwEWgswQKMG0=";
+
+  meta = common.meta // {
+    mainProgram = "yt-dlp-web-ui";
+  };
+}