avoid GC in signal/effect

engine/lib/Signal.ts

@@ -4,17 +4,22 @@ let current: Current = null;
 
 export function createSignal<T>(value: T): [() => T, (value: T) => void] {
 	let innerValue = value;
-	const observers = new Set<() => void>();
+	const observers: Array<Current> = [];
+	const indices = new Map<Current, number>();
 
 	const getter = () => {
-		current !== null && observers.add(current);
+		if (current !== null && !indices.has(current)) {
+			observers.push(current);
+			indices.set(current, observers.length);
+		}
+
 		return innerValue;
 	};
 
 	const setter = (value: T) => {
 		innerValue = value;
-		for (const observer of observers) {
-			observer();
+		for (let i = 0; i < observers.length; i++) {
+			observers[i]!();
 		}
 	};