perf: Redis 操作优化，移除号池 key 列表的 Usage 聚合查询

- 号池 key 列表移除 Usage 表聚合查询(total_tokens/total_cost_usd)，消除慢 SQL
- cooldown 计数从 SCAN 改为 SCARD (O(1))，通过 cooldown_idx SET 维护索引
- 读路径 Lua 脚本移除 ZREMRANGEBYSCORE，清理移至写路径减少开销
- affinity 清理从 KEYS 改为 SCAN 分批删除，invalidate_all_for_provider 改用 pipeline 批量 MGET+UNLINK
- 缓存监控页添加清除按钮 loading 状态，Redis SCAN 并发限制为 4
- 提取 redis_utils 模块统一 SCAN+批量删除逻辑
- 调度热路径跳过 cooldown TTL 查询，account_state 预计算移出循环

src/core/redis_utils.py

@@ -0,0 +1,54 @@
+"""Redis batch-delete utilities.
+
+Provides SCAN-based pattern deletion with UNLINK preference to minimise
+blocking on the Redis server.  Used by cache monitoring and affinity
+manager modules.
+"""
+
+from __future__ import annotations
+
+from typing import Any
+
+from src.core.logger import logger
+
+# Defaults matching existing usage across the codebase.
+DEFAULT_SCAN_BATCH_SIZE = 200
+DEFAULT_DELETE_BATCH_SIZE = 500
+
+
+async def delete_redis_keys(redis: Any, keys: list[str]) -> int:
+    """Batch-delete Redis keys, preferring UNLINK over DELETE."""
+    if not keys:
+        return 0
+
+    try:
+        unlink = getattr(redis, "unlink", None)
+        if callable(unlink):
+            return int(await unlink(*keys))
+    except Exception as exc:
+        logger.debug("Redis UNLINK failed, falling back to DELETE: {}", exc)
+
+    return int(await redis.delete(*keys))
+
+
+async def scan_delete_pattern(
+    redis: Any,
+    pattern: str,
+    *,
+    scan_batch_size: int = DEFAULT_SCAN_BATCH_SIZE,
+    delete_batch_size: int = DEFAULT_DELETE_BATCH_SIZE,
+) -> int:
+    """SCAN + batch-delete keys matching *pattern* without blocking Redis."""
+    deleted_count = 0
+    cursor: int | str = 0
+    while True:
+        cursor, keys = await redis.scan(cursor=cursor, match=pattern, count=scan_batch_size)
+        if keys:
+            for i in range(0, len(keys), delete_batch_size):
+                batch = keys[i : i + delete_batch_size]
+                deleted_count += await delete_redis_keys(redis, batch)
+
+        if int(cursor) == 0:
+            break
+
+    return deleted_count