• serializes beaconState into chunks via SszByteArrayChunksWriter (currently hardcoded to 8MiB chunk sizes)
• on DB side introduced a KvStoreUnchunkedVariable which stores chunks in a similarly to what we do with columns:
  • the base key (id)->byte stores a byte with the number of chunks (max 255 chunks)
  • chunks are stored as(id,chunkIndex) -> chunk bytes

There is an automatic backward compatibility behavior: if the base (id)->byte returns something bigger than a single byte, than it is considered as a big chunk (essentially the previous storage mode)

TODO:

• verify that this actually improves memory allocations (no more big 256mb single byte array)
• implement an iterator when reading chunks
• trimming: if the variable becomes smaller, previous additional chunks remains on DB (we could not care for BeaconState, it always grows)
• rocksDB implementation
• tests

fixes #9018

Documentation

• I thought about documentation and added the doc-change-required label to this PR if updates are required.

Changelog

• I thought about adding a changelog entry, and added one if I deemed necessary.