Function pacejka_fy 

pub fn pacejka_fy(alpha: f64, b: f64, c: f64, d: f64, e: f64) -> f64

Compute the Pacejka magic formula lateral force Fy.

Parameters follow the standard Pacejka notation.

• alpha — slip angle in radians
• b — stiffness factor
• c — shape factor
• d — peak value
• e — curvature factor

Returns the lateral force as a fraction of normal load (Fy / Fz).