Added flushBuffer() to the AudioSource interface

Author: consuelita

AudioCoder/src/main/java/org/operatorfoundation/audiocoder/WSPRAudioSource.kt

@@ -94,6 +94,14 @@ interface WSPRAudioSource
      */
     suspend fun cleanup()
 
+    /**
+     * Discards all buffered audio samples.
+     * Call immediately before starting a decode collection window to ensure
+     * only time-aligned audio is fed to the decoder.
+     * Default implementation is a no-op for sources that don't buffer.
+     */
+    suspend fun flushBuffer() {}
+
     /**
      * Gets current status and diagnostic information about the audio source.
      *