Function pamoja_trend_with_capacity 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn pamoja_trend_with_capacity(
    capacity: usize,
) -> *mut PamojaTrend

Creates an empty trend estimator over up to capacity readings.

Returns

A handle the caller must release with pamoja_trend_free, or null if capacity is not from 2 to PAMOJA_WINDOW_CAPACITY, since a line needs two readings.

Safety

A returned handle must be freed exactly once.