fix: Add missing HashMap import to task_manager

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Co-Authored-By: Claude <[email protected]>

Author: snowmead

rust-docs-mcp/src/cache/task_manager.rs

@@ -4,6 +4,7 @@
 //! Each caching operation gets a unique task ID and can be monitored, cancelled, or cleared.
 
 use dashmap::DashMap;
+use std::collections::HashMap;
 use std::sync::Arc;
 use std::time::SystemTime;
 use tokio_util::sync::CancellationToken;