Do whispers and doubts about Islam during fasting necessitate expiation, knowing that these whispers did not lead to action or speech, and that the questioner has returned to complete faith?

These whispers do not take the questioner out of Islam, and as long as they are disliked and shunned, they do no harm. Their detestation is a sign of true faith, and striving against them indicates immense good.

Therefore, there is no need to make up fasting days, perform ghusl, or renew one's Islam.

As for the devil's whispers during Ramadan, there is no problem with them. The chaining of devils does not completely prevent their movement, but rather weakens them. It is possible that the chained devils are specifically the rebellious jinn. It is narrated in the Hadith: "When the first night of the month of Ramadan comes, the devils and the rebellious jinn are chained."