[mod] addition of various type hints / engine processors

Continuation of #5147 .. typification of the engine processors.

BTW:

- removed obsolete engine property https_support
- fixed & improved currency_convert
- engine instances can now implement a engine.setup method

[#5147] https://github.com/searxng/searxng/pull/5147

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

searx/settings.yml

@@ -718,7 +718,6 @@ engines:
 
   - name: currency
     engine: currency_convert
-    categories: general
     shortcut: cc
 
   - name: deezer