Function structure_constant 

pub fn structure_constant(a: usize, b: usize, c: usize) -> f64

Returns the totally antisymmetric SU(3) structure constants f^{abc}.

Non-zero values (and their antisymmetric permutations):

• f^{123} = 1
• f^{147} = f^{165} = f^{246} = f^{257} = f^{345} = f^{376} = 1/2
• f^{458} = f^{678} = √3/2

Returns: Function that computes f^{abc} for given indices (1-indexed).