[mod] migrate from Redis to Valkey (#4795)

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: HLFH <gaspard@dhautefeuille.eu>
Co-authored-by: Markus Heiser <markus.heiser@darmarit.de>

searx/search/checker/scheduler.py

@@ -1,11 +1,11 @@
 # SPDX-License-Identifier: AGPL-3.0-or-later
 # pylint: disable=missing-module-docstring
-"""Lame scheduler which use Redis as a source of truth:
-* the Redis key SearXNG_checker_next_call_ts contains the next time the embedded checker should run.
-* to avoid lock, a unique Redis script reads and updates the Redis key SearXNG_checker_next_call_ts.
-* this Redis script returns a list of two elements:
+"""Lame scheduler which use Valkey as a source of truth:
+* the Valkey key SearXNG_checker_next_call_ts contains the next time the embedded checker should run.
+* to avoid lock, a unique Valkey script reads and updates the Valkey key SearXNG_checker_next_call_ts.
+* this Valkey script returns a list of two elements:
    * the first one is a boolean. If True, the embedded checker must run now in this worker.
-   * the second element is the delay in second to wait before the next call to the Redis script.
+   * the second element is the delay in second to wait before the next call to the Valkey script.
 
 This scheduler is not generic on purpose: if more feature are required, a dedicate scheduler must be used
 (= a better scheduler should not use the web workers)
@@ -16,8 +16,8 @@ import time
 from pathlib import Path
 from typing import Callable
 
-from searx.redisdb import client as get_redis_client
-from searx.redislib import lua_script_storage
+from searx.valkeydb import client as get_valkey_client
+from searx.valkeylib import lua_script_storage
 
 
 logger = logging.getLogger('searx.search.checker')
@@ -29,7 +29,7 @@ def scheduler_function(start_after_from: int, start_after_to: int, every_from: i
     """Run the checker periodically. The function never returns.
 
     Parameters:
-    * start_after_from and start_after_to: when to call "callback" for the first on the Redis instance
+    * start_after_from and start_after_to: when to call "callback" for the first on the Valkey instance
     * every_from and every_to: after the first call, how often to call "callback"
 
     There is no issue:
@@ -38,11 +38,11 @@ def scheduler_function(start_after_from: int, start_after_to: int, every_from: i
     """
     scheduler_now_script = SCHEDULER_LUA.open().read()
     while True:
-        # ask the Redis script what to do
+        # ask the Valkey script what to do
         # the script says
         # * if the checker must run now.
         # * how to long to way before calling the script again (it can be call earlier, but not later).
-        script = lua_script_storage(get_redis_client(), scheduler_now_script)
+        script = lua_script_storage(get_valkey_client(), scheduler_now_script)
         call_now, wait_time = script(args=[start_after_from, start_after_to, every_from, every_to])
 
         # does the worker run the checker now?