offchain_worker: RuntimeDescriptor<
    [
        header: {
            digest: DigestItem[];
            extrinsics_root: FixedSizeBinary<32>;
            number: number;
            parent_hash: FixedSizeBinary<32>;
            state_root: FixedSizeBinary<32>;
        },
    ],
    undefined,
>

Starts the off-chain task for given block header.