Usage export lists every running-disk charge, including amounts written off

In GET /v1/usage/export, each sandbox disk_used row now covers all disk usage since the previous row, and its measurements include carried, the fraction of a microdollar carried in from the previous row. A running-disk charge that your balance, cost cap or spending limits could not cover now appears as a row with chargedMicros of 0 and its written_off_micros. Charges are unchanged.