Prior to this commit, `ResponseBodyEmitter` woud accept a single
`Runnable` callback on each of its `onTimeout`, `onError` or
`onCompletion` methods. This would limit the developers' ability to
register multiple sets of callbacks: one for managing the publication of
streaming values, another one for managing other concerns like
keep-alive signals to maintain the connection.
This commit now allows multiple calls to `onTimeout`, `onError` and
`onCompletion` and will register all callbacks accordingly.
Closes gh-33356
761fb8f6c9