Function apply_pingpong 

pub fn apply_pingpong<T: Clone>(frames: &[T], exclude_ends: bool) -> Vec<T>

Apply pingpong transform: duplicate frames in reverse order for forward-backward play.

Given frames [A, B, C], produces:

• exclude_ends=false: [A, B, C, C, B, A]
• exclude_ends=true: [A, B, C, B]

Arguments

• frames - The animation frames (sprite names)
• exclude_ends - If true, don’t duplicate first/last frame in reverse

Returns

A new Vec with the pingpong sequence