trivionomicon: athena-bccr: add support for mirrors

pkgs/athena-bccr/unwrapped.nix

@@ -1,5 +1,7 @@
 {
+  fetchurl,
   lib,
+  mirror ? null,
   requireFile,
   release,
   gaudiHash ? null,
@@ -7,10 +9,20 @@
 }: let
   inherit (release) srcPaths vendor;
 
-  src = requireFile {
-    url = "https://soportefirmadigital.com";
+  url =
+    if mirror != null
+    then "${mirror}/${release.filename}"
+    else "https://soportefirmadigital.com";
+
+  fetchSrc =
+    if mirror != null
+    then fetchurl
+    else requireFile;
+
+  src = fetchSrc {
     name = release.filename;
 
+    inherit url;
     inherit (release) hash;
   };