What is the ruling on the whispers that overwhelm the soul regarding the intention to fast and interrupting it during acts of worship?

All the whispers mentioned have no effect on the validity of worship. The cure for them is to ignore them, turn away from them, and not pay them any mind. So, no matter how much Satan whispers about breaking the intention of fasting, or breaking the fast, or anything else, one must ignore that and cast it aside. The same applies to all other acts of worship such as ablution, ghusl (definition), and prayer. There is no cure for whispers except ignoring them and not paying them any mind.