Import Call Detail Records from CSV — supports any column layout
sim_number,call_type,called_number,tower_id,call_start,call_end,duration_sec 9876543210,CALL,9123456789,TOWER-001,2024-01-15 09:00:00,2024-01-15 09:05:30,330 9876543210,SMS,9876543211,TOWER-001,2024-01-15 09:10:00,,0 9876543210,DATA,,TOWER-002,2024-01-15 10:30:00,2024-01-15 11:00:00,1800