[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/__init__.py

@@ -4,19 +4,22 @@
 Implementations used for bot detection.
 
 """
+from __future__ import annotations
+
+__all__ = ["init", "dump_request", "get_network", "too_many_requests", "ProxyFix"]
+
+
+import valkey
 
 from ._helpers import dump_request
-from ._helpers import get_real_ip
 from ._helpers import get_network
 from ._helpers import too_many_requests
-
-__all__ = ['dump_request', 'get_network', 'get_real_ip', 'too_many_requests']
-
-valkey_client = None
-cfg = None
+from . import config
+from . import valkeydb
+from .trusted_proxies import ProxyFix
 
 
-def init(_cfg, _valkey_client):
-    global valkey_client, cfg  # pylint: disable=global-statement
-    valkey_client = _valkey_client
-    cfg = _cfg
+def init(cfg: config.Config, valkey_client: valkey.Valkey | None):
+    config.set_global_cfg(cfg)
+    if valkey_client:
+        valkeydb.set_valkey_client(valkey_client)