Use a delegate config struct for Option

[db47h]

vm.Option directly set Intsance fields, which is bad, it should use a delegate config structure.

With the recent addition of Ticker where using Option would be safe, we need cater for most use cases before switching to a cfg struct.

For example, a ticker function might need to remove itself, or change the tick interval.

Also need to provide more control over the instance to Go code running it.