Handle to the on-disk block index database (blocks/index/).
Declared in <node/blockstorage.h>
[[guarded_by(0x7fd7532b0148), guarded_by(0x7fd74e9c7098), guarded_by(0x7fd75a26ade8), guarded_by(0x7fd74f16e268), guarded_by(0x7fd74a00d908), guarded_by(0x7fd753265218)]]
std::unique_ptr<kernel::BlockTreeDB> m_block_tree_db;