fix: handle closing outbound stream

[twoeths]

Motivation

• The pushable inside Outbound stream keeps some internal buffers inside, we need to clear them when closing the OutboundStream or it becomes a memory leak if the raw stream is also closed

Description

• End the pushable by calling return() method when closing outbound stram - it's similar to end() but also clearing the internal buffers inside the pushable
• Track the inbound/outbound streams in the metrics