Airspace: tail bound ignores the Loop Bass high-pass's overshoot #235

Airspace's tail_samples may fall short when Loop Bass is up.

_tail_bound in lib/audioeffects/airspace.py counts the loop's laps with laps_to_zero(feedback, excess), using only the Top Cut one-pole's excess. It adds the Loop Bass high-pass's memory to each lap's length, but it throws away that filter's excess (bass_memory, _bass = tone_excess(...)).

A high-pass in a feedback loop can lift a lap's peak above the previous lap's. DigitalDelay and PingPongDelay ran into the same thing with Repeat Cut (#146, fixed in #232). There, the per-lap argument didn't hold, and the bound had to be measured: the worst tail reached 1.35 times the laps the argument predicts.

Nobody has measured Airspace yet. To settle it, sweep Feedback, Loop Bass and the rate the way #232's render tests do, with the chamber at its shortest, and compare where the output reaches exact zero against tail_samples. If it overshoots, apply the same fix as the delays: use a measured factor, and add a render test that fails when the factor is 1.