Fix a memory leak in the ViewTester

The following discussion from !729 (merged) should be addressed:

• @graven started a discussion: (+3 comments)

  please avoid 'naked new', and be explicit about ownership, eg. why not auto viewContext = std::make_unique<EventContext>( getContext().evt(), getContext().slot() ); and on transfer of ownership either std::move or .release() explicitly...

Just tagging you @bwynne as I can't assign this to you explicitly.

On it.

Important to note that "whole event" EventContexts are created and deleted by event loop managers, not the scheduler, and are passed around as bare pointers. Either this change will need to stay factorised from that (may not be possible) or will need to cover them too.

Also note that "sub slot" EventContexts can escape the scheduler via the handling for failed events, so will need to remember to catch them.

mentioned in merge request !732 (merged)

Have now got !732 (merged) working nicely with unique pointers. At this stage probably worth discussing whether to go further and replace all EventContext bare pointers in the IScheduler interface with unique pointers.

Also could remove passing of bare pointers in AvalancheScheduler private methods, similar to !727 (merged)

I understand this is closed by !732 (merged). If so, please close it.

For further changes, I opened #46.

closed