Fix audio codec latency handling (#317)

To avoid buffering audio data multiple times, remove buffer from
malgo audio driver and pass expected codec latency as a codec
parameter.

pkg/codec/opus/params_test.go

@@ -0,0 +1,49 @@
+package opus
+
+import (
+	"fmt"
+	"testing"
+	"time"
+)
+
+func TestLatency_Validate(t *testing.T) {
+	t.Run("Valid", func(t *testing.T) {
+		for _, l := range []Latency{
+			Latency2500us, Latency5ms, Latency10ms, Latency20ms, Latency40ms, Latency60ms,
+		} {
+			if !l.Validate() {
+				t.Errorf("Defined Latency(%v) must be valid", l)
+			}
+		}
+	})
+	t.Run("Invalid", func(t *testing.T) {
+		for _, l := range []Latency{
+			0, Latency(time.Second),
+		} {
+			if l.Validate() {
+				t.Errorf("Latency(%v) must be valid", l)
+			}
+		}
+	})
+}
+
+func TestLatency_samples(t *testing.T) {
+	testCases := []struct {
+		latency    Latency
+		sampleRate int
+		samples    int
+	}{
+		{Latency5ms, 48000, 240},
+		{Latency20ms, 16000, 320},
+		{Latency20ms, 48000, 960},
+	}
+	for _, testCase := range testCases {
+		testCase := testCase
+		t.Run(fmt.Sprintf("%v_%d", time.Duration(testCase.latency), testCase.sampleRate), func(t *testing.T) {
+			samples := testCase.latency.samples(testCase.sampleRate)
+			if samples != testCase.samples {
+				t.Errorf("Expected samples: %d, got: %d", testCase.samples, samples)
+			}
+		})
+	}
+}