[mod] migrate from Redis to Valkey

This patch migrates from `redis==5.2.1` [1] to `valkey==6.1.0` [2].

The migration to valkey is necessary because the company behind Redis has decided
to abandon the open source license. After experiencing a drop in user numbers,
they now want to run it under a dual license again. But this move demonstrates
once again how unreliable the company is and how it treats open source
developers.

To review first, read the docs::

    $ make docs.live

Follow the instructions to remove redis:

- http://0.0.0.0:8000/admin/settings/settings_redis.html

Config and install a local valkey DB:

- http://0.0.0.0:8000/admin/settings/settings_valkey.html

[1] https://pypi.org/project/redis/
[2] https://pypi.org/project/valkey/

Co-authored-by: Markus Heiser <markus.heiser@darmarit.de>

searx/valkeydb.py

@@ -0,0 +1,65 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+"""Implementation of the valkey client (valkey-py_).
+
+.. _valkey-py: https://github.com/valkey-io/valkey-py
+
+This implementation uses the :ref:`settings valkey` setup from ``settings.yml``.
+A valkey DB connect can be tested by::
+
+  >>> from searx import valkeydb
+  >>> valkeydb.initialize()
+  True
+  >>> db = valkeydb.client()
+  >>> db.set("foo", "bar")
+  True
+  >>> db.get("foo")
+  b'bar'
+  >>>
+
+"""
+
+import os
+import pwd
+import logging
+import warnings
+
+import valkey
+from searx import get_setting
+
+
+_CLIENT = None
+logger = logging.getLogger(__name__)
+
+
+def client() -> valkey.Valkey:
+    return _CLIENT
+
+
+def initialize():
+    global _CLIENT  # pylint: disable=global-statement
+    if get_setting('redis.url'):
+        warnings.warn("setting redis.url is deprecated, use valkey.url", DeprecationWarning)
+    valkey_url = get_setting('valkey.url') or get_setting('redis.url')
+    if not valkey_url:
+        return False
+    try:
+        # create a client, but no connection is done
+        _CLIENT = valkey.Valkey.from_url(valkey_url)
+
+        # log the parameters as seen by the valkey lib, without the password
+        kwargs = _CLIENT.get_connection_kwargs().copy()
+        kwargs.pop('password', None)
+        kwargs = ' '.join([f'{k}={v!r}' for k, v in kwargs.items()])
+        logger.info("connecting to Valkey %s", kwargs)
+
+        # check the connection
+        _CLIENT.ping()
+
+        # no error: the valkey connection is working
+        logger.info("connected to Valkey")
+        return True
+    except valkey.exceptions.ValkeyError:
+        _CLIENT = None
+        _pw = pwd.getpwuid(os.getuid())
+        logger.exception("[%s (%s)] can't connect valkey DB ...", _pw.pw_name, _pw.pw_uid)
+    return False