新增 Mjpegplayer 用来播放 Web 流

SHH.MjpegPlayer/GrpcImpls/Core/ConcurrentHashSet.cs

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+using System.Collections.Concurrent;
+
+namespace SHH.MjpegPlayer
+{
+    /// <summary>
+    /// 辅助类：线程安全集合
+    /// </summary>
+    public class ConcurrentHashSet<T> : IEnumerable<T>
+    {
+        private readonly ConcurrentDictionary<T, byte> _dict = new ConcurrentDictionary<T, byte>();
+
+        public void Add(T item) => _dict.TryAdd(item, 0);
+
+        public void Remove(T item) => _dict.TryRemove(item, out _);
+
+        public bool IsEmpty => _dict.IsEmpty;
+
+        public IEnumerator<T> GetEnumerator() => _dict.Keys.GetEnumerator();
+
+        System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() => GetEnumerator();
+    }
+}