[feat] add return value when task finishing

[cejanen]

I added return value from task completion to check if task finished. I dont like much code version bc now all call which doesnt care about finished task (eg success) needs to get value, discartableresult cant be used for closures. Any suggestions rly are welcomed

[cejanen]

@schwarja I tried do another run task method but it generated a lot of boilerplate. So at the end and few attempts I created default handler at chat core.

[cejanen]

@schwarja updated + prepared to merge to dev