runners/converter: Fix thread affinity of currency update timer
Amends 8f164924.
The runner lives in a separate thread, but the currency update timer lives on the main thread. Furthermore, the update timer is owned by the runner, which is not okay because its thread affinity is different. It also means that the event loop on the main thread may not properly clean up its timer list.
In order to fix the issue, this change makes the update timer a child of the runner object. With that, both will have the same thread affinity.