Introduction of a Methyl Group Curbs Metabolism of Pyrido[3,4-d]pyrimidine Monopolar Spindle 1 (MPS1) Inhibitors and Enables the Discovery of the Phase 1 Clinical Candidate N²-(2-Ethoxy-4-(4-methyl-4H-1,2,4-triazol-3-yl)phenyl)-6-methyl-N⁸-neopentylpyrido[3,4-d]pyrimidine-2,8-diamine (BOS172722)