Function cell_update

aiscript-arena/src/metrics.rs:264–266

(c: &Cell<T>, f: impl FnOnce(T) -> T)

// https://github.com/rust-lang/rust/issues/50186
#[inline]
fn cell_update<T: Copy>(c: &Cell<T>, f: impl FnOnce(T) -> T) {
    c.set(f(c.get()))
}

// Computes the `debit_factor` (aka, the amount that debits are multiplied by) from the
// `timing_factor` configured by the user. It should always be > 1.0.