[mod] Z-Library engine: revision of the engine (Paper result)

Revision of the engine / use of the result type Paper as well as other
typifications.

The engine has been placed on inactive because no service is currently
available, or at least not known in the SearXNG community [1]

[1] https://github.com/searxng/searxng/issues/3610

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/settings.yml

@@ -1254,9 +1254,10 @@ engines:
   - name: z-library
     engine: zlibrary
     shortcut: zlib
-    categories: files
     timeout: 7.0
     disabled: true
+    # https://github.com/searxng/searxng/issues/3610
+    inactive: true
 
   - name: library of congress
     engine: loc