Registers a lifecyle callback for when a molecule is released (unmounted).
This lifecycle will be called everytime this molecule that is used for a scope has been released. This helps provide an opportunity to cleanup or stop anything that is internally used.
For example, if your molecule is scoped by some
onUnmount will be called for when “User A” and “User B”
scopes are released.
|A callback to run when a molecule is unmounted