Update Nix package definitions to include webcomix and enhance overlays. Refactor download.nix to utilize buildPythonApplication and streamline dependencies, ensuring proper integration of new packages.

flake.nix

@@ -11,6 +11,7 @@
       pkgs = import nixpkgs {
         inherit system;
         config.allowUnfree = true;
+        overlays = [ inputs.self.overlays.default ];
       };
       generatePackages =
         args:
@@ -29,15 +30,11 @@
     in
     {
       overlays.default = _final: prev: {
-        scrapy = prev.scrapy.overrideAttrs (_old: rec {
-          version = "2.11.2";
-          src = prev.fetchFromGitHub {
-            owner = "scrapy";
-            repo = "scrapy";
-            tag = version;
-            hash = "sha256-EaO1kQ3VSTwEW+r0kSKycOxHNTPwwCVjch1ZBrTU0qQ=";
+        python3Packages = prev.python3Packages.override {
+          overrides = pyself: pysuper: {
+            webcomix = prev.python3Packages.callPackage ./pkgs_pr/webcomix.nix { };
           };
-        });
+        };
       };
       packages.x86_64-linux =
         let