How did the Ten Qira'at originate, given that the Qira'at are seven, and does the difference in Qalun's reading from Nafi' from Warsh's reading from Nafi' constitute a new Qira'ah?

The ten continuous recitations (Qira'at Mutawatirah) are not just seven. Their origin is through reception and chains of transmission (Isnad) back to the Prophet (peace be upon him). The three recitations originated similarly to the seven. The difference between the narrations (Riwayat) of Hafs and Shu'bah from Asim is a difference in narration, not in recitation. This is because Asim taught Hafs with the recitation of Abu Abd al-Rahman al-Sulami from Ali, and he taught Shu'bah with the recitation of Zirr ibn Hubaysh from Ibn Mas'ud.