walletFactory uses virtual objects

[michaelfig]

What is the Problem Being Solved?

Wallet manager and individual wallet backends need to be scalable.

Description of the Design

Do the wholesale migration of the wallet backends to collections of virtual objects.

Security Considerations

Test Plan

[Tartuffo]

@michaelfig Do you want this to be under the #3995 (as it is currently) or #4511 (which is the epic for all of the other virtual objects / collection work)?

[Tartuffo]

This work might get subsumed fully or partially by #4484, or at least much lest work.

[Tartuffo]

Wallet Manager is deprecated, so do we still need to do this?

[warner]

We need to measure the slope: RAM used per provisioned account, and also GC time (because that scales with the size of the object graph, hence RAM). Then we can compare that against the 2GiB per-vat limit (#5953) to estimate how many users can be added before the worker would be killed by the memory limit, and then since it is (supposed to be) a criticalVat, the kernel panics and the chain halts.