An object associated to a resumable that is held internally. The variant ResumableRef::Fresh indicates this
resumable has never been invoked/resumed to. ResumableRef::Invoked indicates this resumable has been
invoked/resumed to at least once.
Represents the state of a possibly interrupted resumable. RunState::Finished represents a resumable that has
executed completely. RunState::Resumable represents a resumable that has ran out of fuel during execution, missing
at least required_fuel units of fuel to continue further execution.