Function policy_from_sensitivity 

pub fn policy_from_sensitivity(
    scores: &[SensitivityScore],
    threshold: f32,
    default_precision: LayerPrecision,
    sensitive_precision: LayerPrecision,
) -> MixedPrecisionPolicy

Build a mixed-precision policy from sensitivity scores.

Layers with sensitivity above threshold are kept at sensitive_precision, while the rest use default_precision.