Introduce derived types of MultiPacket

mirai-core/src/commonMain/kotlin/net.mamoe.mirai/data/Packet.kt

@@ -29,8 +29,19 @@ object NoPacket : Packet {
 /**
  * PacketFactory 可以一次解析多个包出来. 它们将会被分别广播.
  */
-open class MultiPacket<P : Packet>(internal val delegate: List<P>) : List<P> by delegate, Packet {
+interface MultiPacket<out P : Packet> : Packet, Iterable<P>
+
+class MultiPacketByIterable<out P : Packet>(internal val delegate: Iterable<P>) : MultiPacket<P>,
+    Iterable<P> by delegate {
     override fun toString(): String {
-        return "MultiPacket<${this.firstOrNull()?.let { it::class.simpleName } ?: "?"}>"
+        return "MultiPacket"
+    }
+}
+
+class MultiPacketBySequence<out P : Packet>(internal val delegate: Sequence<P>) : MultiPacket<P> {
+    override operator fun iterator(): Iterator<P> = delegate.iterator()
+
+    override fun toString(): String {
+        return "MultiPacket"
     }
 }