Backend interface

Storage backends implement the interface defined in the app/src/modules/storage/storage_backend.h file:

struct storage_backend {
    int (*init)(void);
    int (*store)(const struct storage_data *type, void *data, size_t size);
    int (*peek)(const struct storage_data *type, void *data, size_t size);
    int (*retrieve)(const struct storage_data *type, void *data, size_t size);
    int (*count)(const struct storage_data *type);
    int (*clear)(void);
};