Handle WeakActorRef::upgrade() failure gracefully in EngineActor

[coderabbitai]

Problem

In crates/libtortillas/src/engine/actor.rs around lines 133-134, there's a potential panic when calling actor_ref.upgrade().unwrap() in the TCP and uTP peer stream handling logic.

Current Code

Some(Signal::Message {
   message: Box::new(EngineMessage::IncomingPeer(peer_stream)),
   actor_ref: actor_ref.upgrade().unwrap(),
   reply: None,
   sent_within_actor: true,
})

Issue

If the weak actor reference upgrade fails (returns None), the application will panic. This can happen in legitimate scenarios where the actor has been dropped.

Suggested Fix

Handle the upgrade failure gracefully:

let Some(actor_ref) = actor_ref.upgrade() else {
   error!("Failed to upgrade weak actor reference");
   return None;
};
Some(Signal::Message {
   message: Box::new(EngineMessage::IncomingPeer(peer_stream)),
   actor_ref,
   reply: None,
   sent_within_actor: true,
})

Context

This issue affects both TCP and uTP peer stream handling in the EngineActor::next method.

Backlinks

• Original PR: refactor: High level API for Torrent and Engine #125
• Comment: refactor: High level API for Torrent and Engine #125 (comment)
• Reported by: @artrixdotdev