Command block minecarts do not save execution cooldown to NBT

The bug

Command block minecarts do not execute every tick but instead every 4 ticks. However, their cooldown is not saved to NBT. This means when a world with a command block minecart which is supposed to execute the next tick is closed, it will execute after 4 ticks again after the world is reopened.

How to reproduce

1. Summon a command block minecart

   /summon command_block_minecart
   

2. Inspect its NBT data

   /data get entity @e[type=command_block_minecart,limit=1,sort=nearest]
   

   → There is no tag tracking the execution cooldown