Function evaluate 

pub fn evaluate(budget_remaining: f64, change_rate: f64) -> BarrierResult

Evaluate the barrier certificate at (budget_remaining, change_rate).

Both inputs should be in [0, 1]. Values outside this range are clamped.

Returns a BarrierResult with the barrier value and safety verdict.

Performance

This evaluates a degree-4 polynomial with 15 terms using Horner-like nested evaluation. Expected runtime is well under 30ns on modern hardware.