metal : fix memory leaks due to missing autoreleasepools (#27758)

ggml/src/ggml-metal/ggml-metal-context.m

@@ -84,6 +84,7 @@ struct ggml_metal {
 ggml_metal_t ggml_metal_init(ggml_metal_device_t dev) {
     GGML_LOG_INFO("%s: allocating\n", __func__);
 
+    @autoreleasepool {
 #if TARGET_OS_OSX && !GGML_METAL_NDEBUG
         // Show all the Metal device instances in the system
         NSArray * devices = MTLCopyAllDevices();
@@ -185,6 +186,7 @@ ggml_metal_t ggml_metal_init(ggml_metal_device_t dev) {
 
         return res;
     }
+}
 
 void ggml_metal_free(ggml_metal_t ctx) {
     GGML_LOG_INFO("%s: deallocating\n", __func__);

ggml/src/ggml-metal/ggml-metal-device.m

@@ -778,8 +778,10 @@ void ggml_metal_encoder_free(ggml_metal_encoder_t encoder) {
 }
 
 void ggml_metal_encoder_debug_group_push(ggml_metal_encoder_t encoder, const char * name) {
+    @autoreleasepool {
         [encoder->obj pushDebugGroup:[NSString stringWithCString:name encoding:NSUTF8StringEncoding]];
     }
+}
 
 void ggml_metal_encoder_debug_group_pop (ggml_metal_encoder_t encoder) {
     [encoder->obj popDebugGroup];
@@ -1023,6 +1025,7 @@ ggml_metal_device_t ggml_metal_device_init(int device, int n_devices) {
 
     assert(dev != NULL);
 
+    @autoreleasepool {
         if (dev->mtl_device == nil) {
             dev->mtl_device = MTLCreateSystemDefaultDevice();
 
@@ -1268,6 +1271,7 @@ ggml_metal_device_t ggml_metal_device_init(int device, int n_devices) {
 #endif
             }
         }
+    }
 
     return dev;
 }