[mod] limiter: trusted proxies (#4911)

Replaces `x_for` functionality with `trusted_proxies`. This allows defining
which IP / ranges to trust extracting the client IP address from X-Forwarded-For
and X-Real-IP headers.

We don't know if the proxy chain will give us the proper client
address (REMOTE_ADDR in the WSGI environment), so we rely on reading the headers
of the proxy before SearXNG (if there is one, in that case it must be added to
trusted_proxies) hoping it has done the proper checks. In case a proxy in the
chain does not check the client address correctly, integrity is compromised and
this should be fixed by whoever manages the proxy, not us.

Closes:

- https://github.com/searxng/searxng/issues/4940
- https://github.com/searxng/searxng/issues/4939
- https://github.com/searxng/searxng/issues/4907
- https://github.com/searxng/searxng/issues/3632
- https://github.com/searxng/searxng/issues/3191
- https://github.com/searxng/searxng/issues/1237

Related:

- https://github.com/searxng/searxng-docker/issues/386
- https://github.com/inetol-infrastructure/searxng-container/issues/81

searx/botdetection/ip_limit.py

@@ -45,12 +45,11 @@ from ipaddress import (
 import flask
 import werkzeug
 
-from searx.extended_types import SXNG_Request
-from searx import valkeydb
 from searx.valkeylib import incr_sliding_window, drop_counter
 
 from . import link_token
 from . import config
+from . import valkeydb
 from ._helpers import (
     too_many_requests,
     logger,
@@ -92,12 +91,12 @@ SUSPICIOUS_IP_MAX = 3
 
 def filter_request(
     network: IPv4Network | IPv6Network,
-    request: SXNG_Request,
+    request: flask.Request,
     cfg: config.Config,
 ) -> werkzeug.Response | None:
 
     # pylint: disable=too-many-return-statements
-    valkey_client = valkeydb.client()
+    valkey_client = valkeydb.get_valkey_client()
 
     if network.is_link_local and not cfg['botdetection.ip_limit.filter_link_local']:
         logger.debug("network %s is link-local -> not monitored by ip_limit method", network.compressed)