[nudostarforum] add support (#8664)

Add support for nudostar.com forum (XenForo-based forum site).
This is separate from the existing nudostar.py which handles nudostar.tv.

Supports:
- Thread extraction with pagination
- Individual post extraction
- Authentication via xf_user cookie or username/password
- Internal attachments (both linked and embedded images)
- External image host URLs (queued for recursive processing)

test/results/nudostarforum.py

@@ -0,0 +1,29 @@
+# -*- coding: utf-8 -*-
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 as
+# published by the Free Software Foundation.
+
+from gallery_dl.extractor import nudostarforum
+
+
+__tests__ = (
+{
+    "#url"     : "https://nudostar.com/forum/threads/aspen-rae.106714/",
+    "#category": ("", "nudostarforum", "thread"),
+    "#class"   : nudostarforum.NudostarforumThreadExtractor,
+},
+
+{
+    "#url"     : "https://nudostar.com/forum/threads/aspen-rae.106714/page-2",
+    "#category": ("", "nudostarforum", "thread"),
+    "#class"   : nudostarforum.NudostarforumThreadExtractor,
+},
+
+{
+    "#url"     : "https://nudostar.com/forum/threads/name.12345/post-67890",
+    "#category": ("", "nudostarforum", "post"),
+    "#class"   : nudostarforum.NudostarforumPostExtractor,
+},
+
+)