Investigate DIV behaviour after a speed switch

FF04 - DIV - Divider Register (R/W)

This register is incremented at rate of 16384Hz (~16779Hz on SGB). Writing any value to this register resets it to $00. Additionally, this register is reset when executing the stop instruction, and only begins ticking again once stop mode is exited. This also occurs during a speed switch. (**TODO: how is it affected by the wait after a speed switch?**)