CVS Corp. has asked Massachusetts health authorities to allow it to open medical clinics inside 10 drug stores in the eastern part of the state. The company anticipates having 25 to 30 MinuteClinics in Massachusetts before the end of the year, and eventually more than 100 in the state. In January, state regulators adopted rules to allow in-store clinics in Massachusetts, saying that the facilities would ease the burden on overwhelmed emergency rooms and primary care practices.