Spawn listener tasks non-blocking

[ebma]

Context

Some experiments on the refactorings in #545 showed here, that all the 'xx Listener' tasks spawned are blocking and don't yield for a very long time. As can be seen on the following screenshot, 8 of the listener tasks have a 'Busy' time of about 31s and this accumulated all at the same time (when starting the vault client).

Since our processing power on the pods is very limited, we can't have that many tasks busy in parallel, and the whole process gets stuck.

TODO

Refactor the code so that the spawned tasks either yield or are executed sequentually.

[ebma]

@pendulum-chain/product This is quite urgent as we are still facing issues with running the vault clients on Amplitude.