metal : add opt_step_adamw and op_sum (#16529)

* scaffold to support opt step adamw on metal (not written so far)

* add opt-step-adamw kernel for metal

* pass op->src[4] as a separate buffer to the pipeline

* add bounds check to opt-step-adamw kernel

* complete scaffold for GGML_OP_SUM

* naive GGML_OP_SUM kernel

* remove unwanted comment

* change OP_SUM capability gate

* Add has_simdgroup_reduction to both ops to pass CI

ggml/src/ggml-metal/ggml-metal-impl.h

@@ -544,6 +544,10 @@ typedef struct{
     float    limit;
 } ggml_metal_kargs_glu;
 
+typedef struct {
+    uint64_t np;
+} ggml_metal_kargs_sum;
+
 typedef struct {
     int64_t  ne00;
     int64_t  ne01;
@@ -773,4 +777,8 @@ typedef struct {
     uint64_t nb01;
 } ggml_metal_kargs_argmax;
 
+typedef struct {
+    int64_t  np;
+} ggml_metal_kargs_opt_step_adamw;
+
 #endif // GGML_METAL_IMPL