Adds a closure to be called by the default main loop at regular intervals with second granularity.
func will be called repeatedly every
interval seconds until it
Continue(false). Precise timing is not guaranteed, the timeout may
be delayed by other events.
The default main loop almost always is the main loop of the main thread. Thus, the closure is called on the main thread.
In comparison to
timeout_add_seconds(), this only requires
func to be
FnOnce, and will automatically return