Handle to the on-disk block index database (blocks/index/).
Declared in <node/blockstorage.h>
[[guarded_by(0x7fb95f04c948), guarded_by(0x7fb969da6708), guarded_by(0x7fb96c563158), guarded_by(0x7fb9857a0218), guarded_by(0x7fb96cb95b28), guarded_by(0x7fb95a5b9078)]]
std::unique_ptr<kernel::BlockTreeDB> m_block_tree_db;