[fix] engine & network issues / documentation and type annotations

This patch fixes some quirks and issues related to the engines and the network.
Each engine has its own network and this network was broken for the following
engines[1]:

- archlinux
- bing
- dailymotion
- duckduckgo
- google
- peertube
- startpage
- wikipedia

Since the files have been touched anyway, the type annotaions of the engine
modules has also been completed so that error messages from the type checker are
no longer reported.

Related and (partial) fixed issue:

- [1] https://github.com/searxng/searxng/issues/762#issuecomment-1605323861
- [2] https://github.com/searxng/searxng/issues/2513
- [3] https://github.com/searxng/searxng/issues/2515

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

docs/admin/engines/settings.rst

@@ -397,14 +397,26 @@ Communication with search engines.
   Global timeout of the requests made to others engines in seconds.  A bigger
   timeout will allow to wait for answers from slow engines, but in consequence
   will slow SearXNG reactivity (the result page may take the time specified in the
-  timeout to load). Can be override by :ref:`settings engine`
+  timeout to load).  Can be override by ``timeout`` in the :ref:`settings engine`.
 
 ``useragent_suffix`` :
   Suffix to the user-agent SearXNG uses to send requests to others engines.  If an
   engine wish to block you, a contact info here may be useful to avoid that.
 
+.. _Pool limit configuration: https://www.python-httpx.org/advanced/#pool-limit-configuration
+
+``pool_maxsize``:
+  Number of allowable keep-alive connections, or ``null`` to always allow.  The
+  default is 10.  See ``max_keepalive_connections`` `Pool limit configuration`_.
+
+``pool_connections`` :
+  Maximum number of allowable connections, or ``null`` # for no limits.  The
+  default is 100.  See ``max_connections`` `Pool limit configuration`_.
+
 ``keepalive_expiry`` :
-  Number of seconds to keep a connection in the pool. By default 5.0 seconds.
+  Number of seconds to keep a connection in the pool.  By default 5.0 seconds.
+  See ``keepalive_expiry`` `Pool limit configuration`_.
+
 
 .. _httpx proxies: https://www.python-httpx.org/advanced/#http-proxying
 
@@ -429,15 +441,6 @@ Communication with search engines.
   Number of retry in case of an HTTP error.  On each retry, SearXNG uses an
   different proxy and source ip.
 
-``retry_on_http_error`` :
-  Retry request on some HTTP status code.
-
-  Example:
-
-  * ``true`` : on HTTP status code between 400 and 599.
-  * ``403`` : on HTTP status code 403.
-  * ``[403, 429]``: on HTTP status code 403 and 429.
-
 ``enable_http2`` :
   Enable by default. Set to ``false`` to disable HTTP/2.
 
@@ -455,6 +458,11 @@ Communication with search engines.
 ``max_redirects`` :
   30 by default. Maximum redirect before it is an error.
 
+``using_tor_proxy`` :
+  Using tor proxy (``true``) or not (``false``) for all engines.  The default is
+  ``false`` and can be overwritten in the :ref:`settings engine`
+
+
 
 .. _settings categories_as_tabs:
 
@@ -522,13 +530,14 @@ engine is shown.  Most of the options have a default value or even are optional.
         use_official_api: true
         require_api_key: true
         results: HTML
-     enable_http: false
+
+     # overwrite values from section 'outgoing:'
      enable_http2: false
      retries: 1
-     retry_on_http_error: true # or 403 or [404, 429]
      max_connections: 100
      max_keepalive_connections: 10
      keepalive_expiry: 5.0
+     using_tor_proxy: false
      proxies:
        http:
          - http://proxy1:8080
@@ -539,6 +548,11 @@ engine is shown.  Most of the options have a default value or even are optional.
          - socks5://user:password@proxy3:1080
          - socks5h://user:password@proxy4:1080
 
+     # other network settings
+     enable_http: false
+     retry_on_http_error: true # or 403 or [404, 429]
+
+
 ``name`` :
   Name that will be used across SearXNG to define this engine.  In settings, on
   the result page...
@@ -579,7 +593,8 @@ engine is shown.  Most of the options have a default value or even are optional.
   query all search engines in that category (group).
 
 ``timeout`` : optional
-  Timeout of the search with the current search engine.  **Be careful, it will
+  Timeout of the search with the current search engine.  Overwrites
+  ``request_timeout`` from :ref:`settings outgoing`.  **Be careful, it will
   modify the global timeout of SearXNG.**
 
 ``api_key`` : optional
@@ -615,6 +630,37 @@ engine is shown.  Most of the options have a default value or even are optional.
   - ``ipv4`` set ``local_addresses`` to ``0.0.0.0`` (use only IPv4 local addresses)
   - ``ipv6`` set ``local_addresses`` to ``::`` (use only IPv6 local addresses)
 
+``enable_http`` : optional
+  Enable HTTP for this engine (by default only HTTPS is enabled).
+
+``retry_on_http_error`` : optional
+  Retry request on some HTTP status code.
+
+  Example:
+
+  * ``true`` : on HTTP status code between 400 and 599.
+  * ``403`` : on HTTP status code 403.
+  * ``[403, 429]``: on HTTP status code 403 and 429.
+
+``proxies`` :
+  Overwrites proxy settings from :ref:`settings outgoing`.
+
+``using_tor_proxy`` :
+  Using tor proxy (``true``) or not (``false``) for this engine.  The default is
+  taken from ``using_tor_proxy`` of the :ref:`settings outgoing`.
+
+``max_keepalive_connection#s`` :
+  `Pool limit configuration`_, overwrites value ``pool_maxsize`` from
+   :ref:`settings outgoing` for this engine.
+
+``max_connections`` :
+  `Pool limit configuration`_, overwrites value ``pool_connections`` from
+  :ref:`settings outgoing` for this engine.
+
+``keepalive_expiry`` :
+  `Pool limit configuration`_, overwrites value ``keepalive_expiry`` from
+  :ref:`settings outgoing` for this engine.
+
 .. note::
 
    A few more options are possible, but they are pretty specific to some