fix(usage): 抽取 ElapsedTimeText 组件、缩短缓存 TTL 提升实时性，修复 _KeyCandidate slots

- 将 UsageRecordsTable 中的内联计时逻辑抽取为独立的 ElapsedTimeText 组件
- usage records 缓存 TTL 从 15s 降为 3s，全局自动刷新间隔从 5s 改为 3s 并默认开启
- 补充 PoolManager._KeyCandidate 缺失的 __slots__ 字段

src/services/provider/pool/manager.py

@@ -302,12 +302,20 @@ class PoolManager:
             )
 
         class _KeyCandidate:
-            __slots__ = ("key", "is_skipped", "skip_reason")
+            __slots__ = (
+                "key",
+                "is_skipped",
+                "skip_reason",
+                "_pool_extra_data",
+                "_pool_scheduling_trace",
+            )
 
             def __init__(self, key: ProviderAPIKey) -> None:
                 self.key = key
                 self.is_skipped = False
                 self.skip_reason: str | None = None
+                self._pool_extra_data: dict | None = None
+                self._pool_scheduling_trace: PoolSchedulingTrace | None = None
 
         wrappers = [_KeyCandidate(k) for k in keys]
         reordered_wrappers = await self.reorder_candidates(session_uuid, wrappers)  # type: ignore[arg-type]