[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/engines/valkey_server.py

@@ -0,0 +1,99 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+"""Valkey is an open source (BSD licensed), in-memory data structure (key value
+based) store.  Before configuring the ``valkey_server`` engine, you must install
+the dependency valkey_.
+
+Configuration
+=============
+
+Select a database to search in and set its index in the option ``db``.  You can
+either look for exact matches or use partial keywords to find what you are
+looking for by configuring ``exact_match_only``.
+
+Example
+=======
+
+Below is an example configuration:
+
+.. code:: yaml
+
+  # Required dependency: valkey
+
+  - name: myvalkey
+    shortcut : rds
+    engine: valkey_server
+    exact_match_only: false
+    host: '127.0.0.1'
+    port: 6379
+    enable_http: true
+    password: ''
+    db: 0
+
+Implementations
+===============
+
+"""
+
+import valkey  # pylint: disable=import-error
+
+from searx.result_types import EngineResults
+
+engine_type = 'offline'
+
+# valkey connection variables
+host = '127.0.0.1'
+port = 6379
+password = ''
+db = 0
+
+# engine specific variables
+paging = False
+exact_match_only = True
+
+_valkey_client = None
+
+
+def init(_engine_settings):
+    global _valkey_client  # pylint: disable=global-statement
+    _valkey_client = valkey.StrictValkey(
+        host=host,
+        port=port,
+        db=db,
+        password=password or None,
+        decode_responses=True,
+    )
+
+
+def search(query, _params) -> EngineResults:
+    res = EngineResults()
+
+    if not exact_match_only:
+        for kvmap in search_keys(query):
+            res.add(res.types.KeyValue(kvmap=kvmap))
+        return res
+
+    kvmap: dict[str, str] = _valkey_client.hgetall(query)
+    if kvmap:
+        res.add(res.types.KeyValue(kvmap=kvmap))
+    elif " " in query:
+        qset, rest = query.split(" ", 1)
+        for row in _valkey_client.hscan_iter(qset, match='*{}*'.format(rest)):
+            res.add(res.types.KeyValue(kvmap={row[0]: row[1]}))
+    return res
+
+
+def search_keys(query) -> list[dict]:
+    ret = []
+    for key in _valkey_client.scan_iter(match='*{}*'.format(query)):
+        key_type = _valkey_client.type(key)
+        res = None
+
+        if key_type == 'hash':
+            res = _valkey_client.hgetall(key)
+        elif key_type == 'list':
+            res = dict(enumerate(_valkey_client.lrange(key, 0, -1)))
+
+        if res:
+            res['valkey_key'] = key
+            ret.append(res)
+    return ret