Per-context signal storage persistence instance interface. Scoped to either backtest or live mode (one instance per mode).
Each stored signal is keyed by its signal.id and the read operation
iterates over all stored entries to return them as an array.
Custom adapters should implement this interface to override the default file-based signal storage behavior.
waitForInit: (initial: boolean) => Promise<void>
Initialize storage for this mode.
readStorageData: () => Promise<StorageData>
Read all persisted signals by iterating storage keys.
writeStorageData: (signals: StorageData) => Promise<void>
Write signals to storage. Each signal is keyed by its signal.id.