feat: Add the FDv2 data system orchestrator

[beekld]

Summary

Adds the FDv2 orchestrator, the DataSystem implementation that owns the
in-memory store and keeps it populated. It runs an initializer phase to obtain
a basis, then a synchronizer phase for ongoing changes.

The initializer phase tries each initializer in order until one produces a
basis. The synchronizer phase then runs one synchronizer at a time and rotates
between them on three triggers:

• A fallback timer advances to the next synchronizer after a sustained
  interruption.
• A recovery timer returns to the primary synchronizer after the recovery
  interval.
• A terminal error blocks a synchronizer and advances past it.

Initialization is signaled as complete on the first basis and as failed once
every source is exhausted without one, because the client's initialization path
already resolves to success or failure. Synchronizer status transitions are
logged, with interruptions at info (not repeated while ongoing) and terminal
errors at warn.