CancelOnProgress is used as the return value of a Poller's onProgress method.
When a user invokes onProgress, they're required to pass in a function that will be
called as a callback with the new data received each time the poll operation is updated.
onProgress returns a function that will prevent any further update to reach the original callback.
PollProgressCallback is the type of the callback functions sent to onProgress.
These functions will receive a TState that is defined by your implementation of
the Poller class.
CancelOnProgress is used as the return value of a Poller's onProgress method. When a user invokes onProgress, they're required to pass in a function that will be called as a callback with the new data received each time the poll operation is updated. onProgress returns a function that will prevent any further update to reach the original callback.