Add flash attention

VoiceInk/Whisper/LibWhisper.swift

@@ -126,6 +126,10 @@ actor WhisperContext {
         var params = whisper_context_default_params()
         #if targetEnvironment(simulator)
         params.use_gpu = false
+        logger.info("Running on the simulator, using CPU")
+        #else
+        params.flash_attn = true // Enable flash attention for Metal
+        logger.info("Flash attention enabled for Metal")
         #endif
         
         let context = whisper_init_from_file_with_params(path, params)