Function count_flows_in_file 

pub fn count_flows_in_file(
    path: &Path,
    filter: &Filter,
    bpf: Option<&BpfExpr>,
    unidirectional: bool,
) -> Result<HashMap<u64, u64>, PcapError>

Count packets per flow ID in a single streaming pass over path.

Applies filter and bpf to each packet (caller must clear filter.flow_ids to avoid circular exclusion). Non-IP packets (no flow key) are not counted.

Returns a map from flow ID → packet count.

Errors

Returns ToolkitPcapError on I/O or parse failure.