demo-apps: kvstore, queue, and openraft_kv

[andrussal]

This PR adds the first set of example applications to logos-blockchain-testing:

• kvstore
• queue
• openraft_kv

These examples are here for two reasons. They give the testing framework real integrations to evolve against, and they give users working code that shows how an application is structured around TF.

This first PR covers the baseline clustered-app path and adds one consensus-backed example. The follow-up PRs add protocol-oriented and more specialized examples.

Review note

These example PRs do not need critical review. The goal is to get useful example integrations into the repo and improve them from there.

What this PR covers

• kvstore is the simplest end-to-end clustered app
• queue applies the same structure to producer/consumer workloads
• openraft_kv applies the same overall TF structure to a small OpenRaft-backed replicated key-value service with leader failover

This PR establishes the basic clustered-app path and adds one consensus-backed failover example.

Integration shape

Each app is split into four parts:

• Node binary — the application itself
• TF integration — the code that connects the app to TF
• Workloads and expectations — reusable behavior and checks
• Example binaries — small programs that run one sample scenario