Function parse_mermaid_config 

fn parse_mermaid_config(
    value: Option<&Value>,
    default: MermaidConfig,
) -> MermaidConfig

Parses the [mermaid] configuration section.

• auto_scale: float (or int) used by Mermaid renderer for scaling
• max_ratio: float in range (0..=1.0] specifying maximum ratio (clamped to 1.0)