Proposal: Sync Writer API about js-car

[Gozala]

I closed #68 as this provides more adequate API with a lot more predictable memory profile.

[Gozala]

Quoting relevant comment from #68

It wouldn't really even need a byteLength argument because it's going to be holding on to a list of Uint8Arrays anyway and it just needs to create the header when it gets the roots and spit that out first. Nothing about the bytes that it buffers is impacted by the length of the header. You just get a one-shot addRoots() call to open the flood gates.

This is interesting point! In our use cases we generally know how many roots we'll have ahead of time even though we do not know what they're going to be. So it's fairly easy to tell how much memory needs to be allocated to fit the roots. And doing so would allow writing into buffer without having to hold onto blocks freeing memory sooner.

However if number of roots is unknown ahead of writes not having to allocate space is definitely going to be a better option. Given known use cases, I would still suggest going with proposed API one with unknown roots could easily be build as layer on top when/if desired.