feat: create new core data & blockstore that acts as a cache/buffered store

see https://github.com/ipfs/helia-http-gateway/issues/18

We should be able to use a store like so:

```
import { BufferedBlockstore, MemoryBlockstore } from 'blockstore-core'
import { LevelBlockstore } from 'blockstore-level'

const myBlockStore = new BufferedBlockstore(new MemoryBlockstore(), new LevelBlockstore('path'), {})
```

That would take any blockstore as a "fronting" blockstore, and another blockstore as a "backing" blockstore, and would use the front blockstore for immediate writes (cache), and flush that data to the backing blockstore according to some criteria.

This should work similar to https://github.com/ChainSafe/lodestar/blob/unstable/packages/beacon-node/src/network/peers/datastore.ts?rgh-link-date=2023-10-19T14%3A35%3A02Z#L71 but be more generic (i.e. not just for peer data)