fix: 治理 Prometheus 指标基数爆炸和内存缓存无界增长

- 删除高基数标签 key_id/model，移除未使用的指标 concurrency_slots_in_use/streaming_request_duration_seconds
- HTTP 客户端池：命名客户端添加 LRU 淘汰上限，tunnel 客户端添加 LRU 淘汰和 last_used_time 追踪
- ResilienceManager：last_errors 改用 deque(maxlen)，error_stats/circuit_breakers 添加上限淘汰
- HealthMonitor：_circuit_history 改用 deque(maxlen)
- ProviderHealthTracker：清理已无记录的过期 key
- PrometheusPlugin：动态指标数量添加上限，超限后拒绝创建
- 中间件使用路由模板替代实际路径，防止动态路径段导致标签爆炸

src/plugins/monitor/prometheus.py

@@ -39,6 +39,7 @@ class PrometheusPlugin(MonitorPlugin):
 
         # 指标注册表
         self._metrics: dict[str, Any] = {}
+        self._max_dynamic_metrics: int = 100  # 动态创建的指标数上限
         self._buffer: list[Metric] = []
         self._lock = asyncio.Lock()
         self._flush_task: asyncio.Task | None = None  # 跟踪后台任务
@@ -140,9 +141,12 @@ class PrometheusPlugin(MonitorPlugin):
 
     def _get_or_create_metric(
         self, name: str, metric_type: MetricType, labels: list[str] | None = None
-    ) -> Any:
-        """获取或创建指标"""
+    ) -> Any | None:
+        """获取或创建指标，超过上限后拒绝创建新指标"""
         if name not in self._metrics:
+            if len(self._metrics) >= self._max_dynamic_metrics:
+                logger.warning("Prometheus dynamic metrics limit reached, dropping: {}", name)
+                return None
             labels = labels or []
             if metric_type == MetricType.COUNTER:
                 self._metrics[name] = Counter(name, f"Auto-created counter {name}", labels)
@@ -153,7 +157,7 @@ class PrometheusPlugin(MonitorPlugin):
             elif metric_type == MetricType.SUMMARY:
                 self._metrics[name] = Summary(name, f"Auto-created summary {name}", labels)
 
-        return self._metrics[name]
+        return self._metrics.get(name)
 
     async def record_metric(self, metric: Metric) -> None:
         """记录单个指标"""
@@ -190,6 +194,8 @@ class PrometheusPlugin(MonitorPlugin):
                 # 创建新的计数器
                 label_names = list(labels.keys()) if labels else []
                 metric = self._get_or_create_metric(name, MetricType.COUNTER, label_names)
+                if metric is None:
+                    return
                 if labels:
                     metric.labels(**labels).inc(value)
                 else:
@@ -212,6 +218,8 @@ class PrometheusPlugin(MonitorPlugin):
                 # 创建新的仪表
                 label_names = list(labels.keys()) if labels else []
                 metric = self._get_or_create_metric(name, MetricType.GAUGE, label_names)
+                if metric is None:
+                    return
                 if labels:
                     metric.labels(**labels).set(value)
                 else:
@@ -239,11 +247,15 @@ class PrometheusPlugin(MonitorPlugin):
                 # 创建新的直方图
                 label_names = list(labels.keys()) if labels else []
                 if buckets:
+                    if len(self._metrics) >= self._max_dynamic_metrics:
+                        return
                     metric = Histogram(
                         name, f"Auto-created histogram {name}", label_names, buckets=buckets
                     )
                 else:
                     metric = self._get_or_create_metric(name, MetricType.HISTOGRAM, label_names)
+                if metric is None:
+                    return
                 self._metrics[name] = metric
 
                 if labels: