Function ordinal_pattern_3 

pub fn ordinal_pattern_3(a: f32, b: f32, c: f32) -> usize

Classify the ordinal pattern of a triplet (a, b, c) into one of 6 indices.

Returns 0–5 encoding the rank-order permutation:

Index	Order	Description
0	a ≤ b ≤ c	Rising
1	a ≤ c < b	Rise-then-fall
2	c < a ≤ b	Fall-then-rise
3	b < a ≤ c	Dip-then-climb
4	b ≤ c < a	Descent with mid-bounce
5	c < b < a	Falling

Ties are broken by index order (left ≤ right).