Bug: txHandler and txSync do not start after node catching up

[algonautshant]

The txHandler and txSyncer are stopped when catching up from a catchpoint, and start again afterwards.

But they never really start. The main loop of these services rely on a context to stop. That context is canceled when stopping. Then, when the services are started again, the contexts remain canceled, which leads for the service to immediately end.

The fix is to create a new context when starting these services.

txSync has another control mechanism to wait starting the loop, which should be handled for "re"-start.