Function run_ac_log_loss_mixture_bytes 

pub fn run_ac_log_loss_mixture_bytes(
    data: &[u8],
    spec: &MixtureSpec,
    out_prefix: impl AsRef<Path>,
) -> Result<AcLogLossRunSummary>

Run exact AC/log-loss diagnostics for a byte sequence under a mixture spec.

This function validates spec, evaluates mixture and expert probabilities at each input position, and writes three TSV artifacts using out_prefix:

• out_prefix.trace.tsv: per-position diagnostics and expert rows
• out_prefix.nodes.tsv: flattened node metadata for trace column mapping
• out_prefix.summary.tsv: aggregate totals and averages

The returned summary includes key scalar metrics and the concrete output paths.