API for writing MapStore to recorders

[turadg]

What is the Problem Being Solved?

It's intuitive for a contract developer to serialize the data in a collection and write it out in a recorder to vstorage. But it doesn't scale. For example, Kryha/KREAd#17

The solution is generally to write out multiple nodes, but this is a burden on the developer and multiple implementations leave room for errors.

Description of the Design

A common utility for serializing durable storage across multiple storage nodes.

E.g. given a MapStore it puts the data at each key under a node with that key as the subpath. For efficiency, it can wrap the MapStore with methods (like Recorder wraps PublishKit) so that it's aware when items are deleted are added to know what storage operations to perform.

We might also have helpers for writing out a SetStore or vector/array but those can be other tickets.

Security Considerations

Abstraction

Scaling Considerations

Should improve use of best practices

Test Plan

Unit tests

Upgrade Considerations

The collection is local to the vat and this code will be too. Does not complicate upgrade.