- Remove `print_job_timer.stop()` from `disable_all_heaters`
- Call `print_job_timer.stop()` for relevant `disable_all_heaters()`.
- Split up `kill()` for watchdog interrupt safety
- Fix an error in the return value of `sd_mmc_spi_read_capacity` which was causing the host OS to read beyond the last sector in the card.
- Clean up the USB flashdrive code and add better debugging.