A Convenient Synthesis and Biological Research of Novel 5,6,7,8-Tetrahydro-1,6-naphthyridin-2(1H)-one Derivatives Hydrochloride as Cytotoxic Agents: A Convenient Synthesis and Biological Research of Novel 5,6,7,8-Tetrahydro-1,6-naphthyridin-2(1H)-one Derivatives Hydrochloride as Cytotoxic Agents