Function print_gathered_header 

pub fn print_gathered_header(
    nodes: &str,
    count: usize,
    out: &mut impl Write,
) -> Result<()>

Print gathered output with a node header.

Mirrors Display.format_header() from the Python oracle: the node count is appended as (N) only when more than one node is gathered (node_count at standard verbosity).

---------------
node[1-3] (3)
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hello world