feat(context): Reuse EmptyContext instance on deflation

Author: PerfectSlayer

components/context/src/main/java/datadog/context/SingletonContext.java

@@ -32,7 +32,7 @@ public <V> Context with(ContextKey<V> secondKey, @Nullable V secondValue) {
     int secondIndex = secondKey.index;
     if (this.index == secondIndex) {
       return secondValue == null
-          ? new EmptyContext()
+          ? EmptyContext.INSTANCE
           : new SingletonContext(this.index, secondValue);
     } else {
       Object[] store = new Object[max(this.index, secondIndex) + 1];