Tree walk splitter can throw error getting the block links about carbites

[alanshaw]

According to https://stackoverflow.com/questions/34430182/too-many-properties-in-a-js-object the propery limit is 65,535. If you have an array with more than 65,535 CIDs then you'll hit this.

This could happen if you create a CBOR node with tons of children like randomCar will build if you give it a target size that's big enough.

https://github.com/alanshaw/carbites/blob/6f14737f77921fef0b4fbfc67bac6d7ea3fb0690/test/_helpers.js#L19

In practice IPFS will only create pb nodes with 174 children max, but Block#links should be updated to iterate over arrays instead of using Object.entries.