Macro stringify_variables 

macro_rules! stringify_variables {
    ($labels:expr, $separator:expr) => { ... };
    ($labels:expr, $separator:expr, $line_length:expr) => { ... };
}

A macro to concatenate a list of variable labels into a formatted string.

This macro accepts a list of labels and a separator, with an optional third argument to control line breaks. If a line length is provided, a newline is inserted after every line_length elements.

Arguments

• $labels - A list of variable labels (Vec<String>).
• $separator - A separator string to join the labels.
• $line_length (optional) - An optional maximum number of labels per line.

Returns

A formatted string where labels are concatenated with the given separator.