Function merge_child_state 

pub fn merge_child_state(
    parent: &mut HashMap<Address, Account, FbBuildHasher<20>>,
    child: HashMap<Address, Account, FbBuildHasher<20>>,
)

Merges a child’s returned account state into its suspended parent.

Preserve parent warmth and original storage values, import child account flags and current values, and retain untouched parent accounts and slots. Newly loaded accounts and slots keep their child metadata. This operates on the EVM’s returned state, not on an unfiltered write set; the caller retains responsibility for execution errors and family-specific reconciliation.