feat(anvil): add Kick lock with offset audition

Anvil gets a sidechain input named Kick. With Kick lock on, kicks are
found on the undelayed sidechain, so with the lookahead each hit ducks
the sub (Duck, Release) when the delayed kick plays and restarts the sub
at Phase, shifted by Offset (-30 to +30 ms, also before the kick).

The Audition steps the offset from -30 to +30 ms, 4 kicks each, and
measures how kick and sub sum below 150 Hz after each hit; Keep takes the
offset heard. On a 55 Hz kick burst against a 55 Hz sub the sum peaks at
0 ms (+2.4 dB) and nearly again one period away (+/-20 ms), so the bars
check the choice by ear rather than make it.

plugins/anvil/plugin/tests/host.rs

@@ -83,8 +83,9 @@ fn effect_ports_state_latency_and_audio_lifecycle() {
         let ports = p.get_extension.unwrap()(plugin, CLAP_EXT_AUDIO_PORTS.as_ptr())
             as *const clap_plugin_audio_ports;
         assert!(!ports.is_null());
+        // Main input plus the kick sidechain; one output.
+        assert_eq!((*ports).count.unwrap()(plugin, true), 2);
         assert_eq!((*ports).count.unwrap()(plugin, false), 1);
-        assert_eq!((*ports).count.unwrap()(plugin, true), 1);
         let latency = p.get_extension.unwrap()(plugin, CLAP_EXT_LATENCY.as_ptr())
             as *const clap_plugin_latency;
         assert!(!latency.is_null());
@@ -108,6 +109,13 @@ fn effect_ports_state_latency_and_audio_lifecycle() {
             .params
             .insert("level".into(), ParamValue::F32(-14.));
         envelope.params.insert("octave".into(), ParamValue::I32(-1));
+        envelope.params.insert("ghost".into(), ParamValue::F32(40.));
+        envelope
+            .params
+            .insert("kick_lock".into(), ParamValue::Bool(true));
+        envelope
+            .params
+            .insert("kick_offset".into(), ParamValue::F32(-7.));
         envelope
             .params
             .insert("snap".into(), ParamValue::Bool(false));
@@ -154,14 +162,26 @@ fn effect_ports_state_latency_and_audio_lifecycle() {
                 let mut left = [0f32; 512];
                 let mut right = [0f32; 512];
                 let mut in_channels = [input_left.as_mut_ptr(), input_right.as_mut_ptr()];
+                // A connected but silent kick sidechain.
+                let (mut kick_left, mut kick_right) = ([0f32; 512], [0f32; 512]);
+                let mut kick_channels = [kick_left.as_mut_ptr(), kick_right.as_mut_ptr()];
                 let mut out_channels = [left.as_mut_ptr(), right.as_mut_ptr()];
-                let incoming = clap_audio_buffer {
-                    data32: in_channels.as_mut_ptr(),
-                    data64: ptr::null_mut(),
-                    channel_count: 2,
-                    latency: 0,
-                    constant_mask: 0,
-                };
+                let incoming = [
+                    clap_audio_buffer {
+                        data32: in_channels.as_mut_ptr(),
+                        data64: ptr::null_mut(),
+                        channel_count: 2,
+                        latency: 0,
+                        constant_mask: 0,
+                    },
+                    clap_audio_buffer {
+                        data32: kick_channels.as_mut_ptr(),
+                        data64: ptr::null_mut(),
+                        channel_count: 2,
+                        latency: 0,
+                        constant_mask: 0,
+                    },
+                ];
                 let mut outgoing_audio = clap_audio_buffer {
                     data32: out_channels.as_mut_ptr(),
                     data64: ptr::null_mut(),
@@ -182,9 +202,9 @@ fn effect_ports_state_latency_and_audio_lifecycle() {
                     steady_time: position as i64,
                     frames_count: frames as u32,
                     transport: ptr::null(),
-                    audio_inputs: &incoming,
+                    audio_inputs: incoming.as_ptr(),
                     audio_outputs: &mut outgoing_audio,
-                    audio_inputs_count: 1,
+                    audio_inputs_count: 2,
                     audio_outputs_count: 1,
                     in_events: &input,
                     out_events: &outgoing,