CASPaxos implementation

CASPaxos has been on our radar for a while.

It'd be a fantastic implementation for "CAS a registry" e.g. for configuration.

Internal for the system use cases include: registry and configuration, perhaps "singleton location" where we could CAS which member is to host the singleton, potentially membership (??? though there'd be various tradeoffs with the convergence one). For end users it'd be a great alternative to do "atomic distributed registry"

The issue names no files, entry points, or tests. Start by surveying the existing registry and configuration mechanisms, then evaluate the proposed singleton-location and membership use cases; done requires an agreed scope and a complete CASPaxos implementation for the selected distributed-registry use case.

Written by the indexing model from the issue text.