feat(US-03): generate 880 Hz sine wave with BeepGenerator

app/src/main/kotlin/net/jeena/pacer/BeepGenerator.kt

@@ -0,0 +1,20 @@
+package net.jeena.pacer
+
+import kotlin.math.sin
+import kotlin.math.PI
+
+object BeepGenerator {
+
+    const val SAMPLE_RATE = 44100
+    const val FREQUENCY = 880.0
+
+    fun generateBeep(durationMs: Int): ShortArray {
+        val numSamples = SAMPLE_RATE * durationMs / 1000
+        val samples = ShortArray(numSamples)
+        for (i in 0 until numSamples) {
+            val angle = 2.0 * PI * FREQUENCY * i / SAMPLE_RATE
+            samples[i] = (sin(angle) * Short.MAX_VALUE).toInt().toShort()
+        }
+        return samples
+    }
+}