Function unbounded_gdn_gate 

pub fn unbounded_gdn_gate(g_raw: f32, dt_bias: f32, a_log: f32) -> f32

2026-09-25: The unbounded Qwen GDN gate, used by the tests to show the two laws diverge.

compute_gdn_gates stores exp(g); this returns g, as the KDA recurrence takes the exponential itself.