As bitcoin approaches 2140, when "the last satoshi is created," how does the protocol handle this operation? Additionally, when people say, "there will never be more than 21 million bitcoins created," does that mean that technically there will not be more than 21 million bitcoins but that there can be slightly more than 21 million and it will never hit 22 million? In other words, is there an asymptote at 21 million, or 22 million, or neither because when the last satoshi is created is the exact same time it technically hits 21 million and the protocol checks and stops coinbase rewards?