[C++] Use weak ref to ClientConnection for timeout task (#12409)
[C++] Use weak ref to ClientConnection for timeout task (#12409)

### Motivation

Fixes #12408. Using a weak reference in the timeout task for `ClientConnection` to break a circular reference dependency between the connection instance and the task.
massakam/pulsar,massakam/pulsar,massakam/pulsar,merlimat/pulsar,merlimat/pulsar,massakam/pulsar,yahoo/pulsar,yahoo/pulsar,merlimat/pulsar,merlimat/pulsar,merlimat/pulsar,yahoo/pulsar,massakam/pulsar,yahoo/pulsar,yahoo/pulsar,yahoo/pulsar,massakam/pulsar,merlimat/pulsar