Continues storage abstraction separation by extracting state management from DataStore into dedicated per-circuit storage instances.

Previously, we introduced the Domain::Storage::State interface. This PR implements the actual storage classes following the same pattern as recovery locks.

Before: DataStore handled state for ALL circuits:

data_store.set_state(config, state)
snapshot = data_store.get_state_snapshot(config)
first_to_transition = data_store.transition_to_color(config, Color::RED)

After: each circuit has its own state storage instance:

state_store = Memory::State.new(clock:, cool_off_time:)  # Per circuit
state_store.set_state(state)  # No config needed - knows its circuit
snapshot = state_store.state_snapshot
first_to_transition = state_store.transition_to_color(Color::RED)

Also introduces Domain::Clock interface with Infrastructure::SystemClock implementation, making time dependencies explicit and testable.

The Redis implementation is composed with FailSafe::State decorator for automatic memory failover, wired in LightBuilder.