frida-gum: dereference listener objects

[ajwerner]

When combined with https://github.com/frida/frida-rust/pull/153, fixes https://github.com/frida/frida-rust/issues/152.

[s1341]

This means that you need to keep references to the returned Listeners alive for as long as you want the hooks to remain, right? That will break a lot of stuff.

[ajwerner]

No Frida increments the ref count when you attach and drops it when you detach. That’s why it was a leak.

[s1341]

Ok. Let's see what CI says.

[s1341]

Merged. Thanks!