op-conductor: Add test to ensure raft state is snapshotted safely

[BrianBland]

Description

Adds a new test which ensures that Raft FSM snapshots used by the op-conductor are not mutated by future applies, and can safely be persisted after a delay.

Tests

See above, test-only change

Additional context

Add any other context about the problem you're solving.

Metadata

• Fixes #[Link to Issue]