Function flatten_call_trace_with_precompiles 

pub fn flatten_call_trace_with_precompiles(
    arena: CallTraceArena,
    out: &mut Vec<DebugNode>,
    precompile_labels: &AddressHashMap<String>,
    contract_names: &[Option<String>],
)

Flattens given [CallTraceArena] into a list of DebugNodes using active precompile labels.

contract_names holds the identified contract name for each arena node, indexed by node index.