use LRUSet to skip already seen event processing

packages/shared/src/LRUSet.ts

@@ -0,0 +1,23 @@
+export default class LRUSet<T> {
+  private set = new Set<T>();
+  private limit: number;
+
+  constructor(limit: number) {
+    this.limit = limit;
+  }
+
+  add(item: T) {
+    if (this.set.size >= this.limit) {
+      this.set.delete(this.set.values().next().value);
+    }
+    this.set.add(item);
+  }
+
+  has(item: T) {
+    return this.set.has(item);
+  }
+
+  values() {
+    return this.set.values();
+  }
+}