Function australian_kt_step 

pub fn australian_kt_step(kt_prev: f64, p: f64) -> f64

One exact step of the AOFM Kt chain: Kt = round₂(Kt₋₁ · (1 + p/100)).

The way to advance a published factor. Because each step rounds, the chain’s value depends on its whole history — stepping from a published Kt is exact where rebuilding from a ratio is a stand-in.