Internal signing provider to use store for private key persistancy

[mjuchli-da]

The signing drivers (-internal as well as -fireblocks) currently use memory to store internal information. We should instead extend the Store interface and provide persistency to the drivers.

The challenge lays in finding the interface definition which enables persistency for all drivers but at the same time offers room for performance. My initial idea of get/setSiginingDriverState(driver: SigningDriver, state: object) is likely not sufficient as it does not allow for partially updating the state, say once a transaction is signed and the corresponding status of the transaction that we track changes.

[mjuchli-da]

Consider to have a separate SigningDriverStore interface within the signing-lib, instead of the generic method(s) on the Store interface.