`Stream Subscriber Plugin` Improve Session Control Flow and Exception Handling

[ata-nas]

Story Form

As a Block Node Engineer
I want to have a clean, easy to maintain and correct subscriber plugin
So that it will run properly

Technical Notes

DEPENDS ON: #1556

• the session is a callable and should generally not catch any exceptions
• this gives the opportunity of the caller to handle an ExecutionException and take proper action, possibly retrying by issuing another session, or closing the session
• throwing exceptions should not be used as control flow inside the session