Configure singleton Downloader

This Downloader instance is used when a datafeed[1] URL is provided, but
will throw an NPE if it isn't configured[2].

[1]: https://github.com/rm-hull/nvd-clojure?tab=readme-ov-file#configuration-options
[2]: rm-hull#182

src/nvd/config.clj

@@ -30,7 +30,7 @@
   (:import
    (java.io File)
    (org.owasp.dependencycheck Engine)
-   (org.owasp.dependencycheck.utils Settings Settings$KEYS)))
+   (org.owasp.dependencycheck.utils Downloader Settings Settings$KEYS)))
 
 (def ^:private string-mappings
   {Settings$KEYS/ANALYZER_NEXUS_URL        [:analyzer :nexus-url]
@@ -209,12 +209,14 @@ You can pass an empty string for an .edn file to be automatically created."
 
         (.setString settings Settings$KEYS/NVD_API_KEY api-key)))
 
-    (-> project
-        (assoc-in [:nvd :data-directory] (.getDataDirectory settings))
-        (assoc :engine      (Engine. settings)
-               :title       (str (app-name project) " " (:version project))
-               :start-time  (System/currentTimeMillis)
-               :config-file config-filename))))
+    (.configure (Downloader/getInstance) settings)
+
+     (-> project
+         (assoc-in [:nvd :data-directory] (.getDataDirectory settings))
+         (assoc :engine      (Engine. settings)
+                :title       (str (app-name project) " " (:version project))
+                :start-time  (System/currentTimeMillis)
+                :config-file config-filename))))
 
 (defn cleanup [project]
   (let [engine ^Engine (:engine project)