fix: 治理 Prometheus 指标基数爆炸和内存缓存无界增长

- 移除 token/latency Prometheus 指标的 model 标签，避免 provider x model 笛卡尔积
- HealthMonitor 滑动窗口从 DB JSON 迁移至进程内存，减少写放大
- ModelCostService 三层缓存增加 500 条上限，超限时清空
- StickyPriority 粘性缓存和健康状态字典增加容量淘汰
- AffinityManager 请求锁字典增加 500 条上限，淘汰空闲锁
- 配额刷新/探测查询使用 defer/load_only 避免加载大 JSON 列
- Alembic 迁移清理 DB 中遗留的 request_results_window 数据
- 同步更新测试适配 batch_get_cooldowns 返回值和批量删除异步化

alembic/versions/20260310_1200_a3f1b7c9d2e4_strip_window_from_health_json.py

@@ -0,0 +1,42 @@
+"""Strip request_results_window from health_by_format JSON.
+
+This data is now maintained in process memory only, no longer persisted to DB.
+
+Revision ID: a3f1b7c9d2e4
+Revises: 2053ab8ed764
+Create Date: 2026-03-10 12:00:00.000000+00:00
+
+"""
+
+from alembic import op
+
+# revision identifiers, used by Alembic.
+revision = "a3f1b7c9d2e4"
+down_revision = "2053ab8ed764"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.execute("""
+        UPDATE provider_api_keys
+        SET health_by_format = (
+            SELECT jsonb_object_agg(
+                fmt_key,
+                fmt_value - 'request_results_window'
+            )
+            FROM jsonb_each(health_by_format) AS x(fmt_key, fmt_value)
+        )
+        WHERE health_by_format IS NOT NULL
+          AND health_by_format != '{}'::jsonb
+          AND EXISTS (
+              SELECT 1
+              FROM jsonb_each(health_by_format) AS x(fmt_key, fmt_value)
+              WHERE fmt_value ? 'request_results_window'
+          )
+    """)
+
+
+def downgrade() -> None:
+    # No-op: window data is rebuilt from scratch on process start
+    pass