Officials in Baltimore plan to open a deeper channel for commercial ships to enter and leave the city’s port starting on Thursday — a significant step toward reopening the major maritime shipping hub that has remained closed to most traffic since the Francis Scott Key Bridge collapsed last month. The new channel will be 35 feet (12 meters) deep, which is a substantial increase over the three other temporary channels established in recent weeks. It puts the cleanup effort slightly ahead of schedule, as officials previously said they hoped to open a channel of that depth by the end of April.