Function btck_chainstate_manager_get_best_entry 

pub unsafe extern "C" fn btck_chainstate_manager_get_best_entry(
    chainstate_manager: *const btck_ChainstateManager,
) -> *const btck_BlockTreeEntry

@brief Get the btck_BlockTreeEntry whose associated btck_BlockHeader has the most known cumulative proof of work.

@param[in] chainstate_manager Non-null. @return The btck_BlockTreeEntry.