Function equal_width 

pub fn equal_width(
    data: &[f64],
    num_symbols: usize,
) -> Result<Vec<u8>, SymbolizeError>

Quantize data into num_symbols equal-width bins.

Bin boundaries are [min, min + w, min + 2w, ...] where w = (max - min) / n. Symbols are 0 ..= num_symbols - 1.

Errors

Returns SymbolizeError if data is empty, num_symbols < 2, or all values are identical (zero-width bins).