perf(cache): 优化缓存下载逻辑并添加性能指标追踪

- 实现了带等待时间统计的缓存锁获取功能
- 新增 get_or_download_with_metrics 方法返回详细的性能指标
- 在 tracing span 中记录锁等待时间、锁获取状态和缓存路径使用情况
- 优化缓存命中路径避免不必要的锁获取操作
- 添加了缓存文件就绪检查和复制功能的独立方法
- 增加了针对缓存锁超时但仍可使用就绪缓存的处理逻辑
- 新增了多个单元测试验证缓存锁定和指标报告功能

handlers/base.py

@@ -682,10 +682,26 @@ class BaseHandler(TaskHandler, ABC):
             },
         ) as span:
             try:
+                lock_wait_ms = 0
+                lock_acquired = False
+                cache_path_used = "unknown"
                 if use_cache:
-                    result = self.material_cache.get_or_download(url, dest, timeout=timeout)
+                    result, cache_metrics = self.material_cache.get_or_download_with_metrics(
+                        url,
+                        dest,
+                        timeout=timeout
+                    )
+                    lock_wait_ms = int(cache_metrics.get("lock_wait_ms", 0))
+                    lock_acquired = bool(cache_metrics.get("lock_acquired", False))
+                    cache_path_used = str(cache_metrics.get("cache_path_used", "unknown"))
                 else:
                     result = storage.download_file(url, dest, timeout=timeout)
+                    cache_path_used = "direct"
+
+                if span is not None:
+                    span.set_attribute("render.file.lock_wait_ms", lock_wait_ms)
+                    span.set_attribute("render.file.lock_acquired", lock_acquired)
+                    span.set_attribute("render.file.cache_path_used", cache_path_used)
 
                 if result:
                     file_size = os.path.getsize(dest) if os.path.exists(dest) else 0