Truce EQ

Truce EQ is one of the in-tree example plugins shipped with the truce framework. It's a 3-band parametric equalizer using biquad filters in Direct Form II Transposed, with logarithmic frequency / Q parameter ranges and per-sample coefficient updates driven from the smoothed parameters.

The DSP runs end-to-end at f64 (`use truce::prelude64::*`). Biquad coefficient computation is precision-sensitive at low Q × low frequency, and the format wrapper widens host f32 to plugin f64 at the block boundary so the math stays in f64 throughout.

Auto-bypass kicks in when a band's gain is within ε of 0 dB, so unused bands cost nothing at runtime.