metal : add f16 and bf16 support for concat operator (#24724)

* metal : add f16 and bf16 support for concat operator

Extend the Metal backend concat operator to support f16 and bf16 tensor
types in addition to the existing f32 and i32 support.

- Template kernel_concat on type T with specializations for float, half,
  bfloat, and int
- Add type-specific pipeline getter ggml_metal_library_get_pipeline_concat()
- Update device support check to allow f16 unconditionally and bf16 when
  device supports bfloat16
- Update dispatch to select the correct kernel specialization by type

Assisted-by: pi:llama.cpp/Qwen3.6-27B

* metal : extend concat operator to support f16, bf16, i8, i16 and i64

Assisted-by: pi:llama.cpp/Qwen3.6-27B

ggml/src/ggml-metal/ggml-metal-device.cpp

@@ -66,7 +66,6 @@ struct ggml_metal_pipeline_with_params ggml_metal_library_get_pipeline_base(ggml
     const char * op_str = "undefined";
     switch (op) {
         case GGML_OP_ADD_ID: op_str = "add_id"; break;
-        case GGML_OP_CONCAT: op_str = "concat"; break;
         default: GGML_ABORT("fatal error");
     };
 
@@ -211,6 +210,21 @@ ggml_metal_pipeline_with_params ggml_metal_library_get_pipeline_repeat(ggml_meta
     return res;
 }
 
+ggml_metal_pipeline_with_params ggml_metal_library_get_pipeline_concat(ggml_metal_library_t lib, ggml_type tsrc) {
+    char base[256];
+    char name[256];
+
+    snprintf(base, 256, "kernel_concat_%s", ggml_type_name(tsrc));
+    snprintf(name, 256, "%s", base);
+
+    ggml_metal_pipeline_with_params res = ggml_metal_library_get_pipeline(lib, name);
+    if (!res.pipeline) {
+        res = ggml_metal_library_compile_pipeline(lib, base, name, nullptr);
+    }
+
+    return res;
+}
+
 ggml_metal_pipeline_with_params ggml_metal_library_get_pipeline_unary(ggml_metal_library_t lib, const ggml_tensor * op) {
     char base[256];
     char name[256];