ref(deps): Drop hard redis-py-cluster dependency to allow redis>=4

clients/python/pyproject.toml

@@ -15,7 +15,6 @@ dependencies = [
     "orjson>=3.10.10",
     "protobuf>=5.28.3",
     "redis>=3.4.1",
-    "redis-py-cluster>=2.1.0",
     "zstandard>=0.18.0",
 ]
 
@@ -34,6 +33,11 @@ dev = [
     "types-protobuf>=5.27.0.20240626,<6.0.0",
 ]
 [project.optional-dependencies]
+# redis<4 does not bundle cluster support; pull in redis-py-cluster (EOL) for it.
+# Not needed on redis>=4.1, which provides redis.RedisCluster natively.
+cluster = [
+    "redis-py-cluster>=2.1.0",
+]
 examples = [
     "click>=8.3",
     "setuptools>=80.0",

clients/python/src/taskbroker_client/scheduler/storage.py

@@ -2,10 +2,16 @@
 
 from collections.abc import Mapping
 from datetime import UTC, datetime
-from typing import Protocol
+from typing import TYPE_CHECKING, Protocol
 
 from redis.client import StrictRedis
-from rediscluster import RedisCluster
+
+if TYPE_CHECKING:
+    try:
+        # redis>=4.1 ships cluster support natively
+        from redis import RedisCluster
+    except ImportError:  # pragma: no cover - redis<4 fallback via the `cluster` extra
+        from rediscluster import RedisCluster
 
 from taskbroker_client.metrics import MetricsBackend
 
@@ -105,9 +111,7 @@ class RunStorage(RunStorageProtocol):
     Redis backed scheduler storage
     """
 
-    def __init__(
-        self, metrics: MetricsBackend, redis: RedisCluster[str] | StrictRedis[str]
-    ) -> None:
+    def __init__(self, metrics: MetricsBackend, redis: RedisCluster | StrictRedis) -> None:
         self._redis = redis
         self._metrics = metrics