vulkan: extend topk_moe to handle sigmoid w/exp_probs_b for nemotron (#18295)

* vulkan: extend topk_moe to handle sigmoid w/exp_probs_b for nemotron

Also handle GGML_OP_SCALE at the end (nemotron, deepseek2).

Fewer pipeline variants and spec constants, just use push constants.

In test_topk_moe, change exp_probs_b to be 1D, matching real networks.

Update test-backend-ops and ggml-backend to allow verifying multiple outputs
in a fusion test (topk_moe has two outputs). Previously only the final node
was verified.

* change test_topk_moe to allow results in arbitrary order

* disable sigmoid fusion for moltenvk

ggml/include/ggml-backend.h

@@ -358,7 +358,7 @@ extern "C" {
     typedef bool (*ggml_backend_eval_callback)(int node_index, struct ggml_tensor * t1, struct ggml_tensor * t2, void * user_data);
 
     // Compare the output of two backends
-    GGML_API bool ggml_backend_compare_graph_backend(ggml_backend_t backend1, ggml_backend_t backend2, struct ggml_cgraph * graph, ggml_backend_eval_callback callback, void * user_data, struct ggml_tensor * test_node);
+    GGML_API bool ggml_backend_compare_graph_backend(ggml_backend_t backend1, ggml_backend_t backend2, struct ggml_cgraph * graph, ggml_backend_eval_callback callback, void * user_data, struct ggml_tensor const * const * test_nodes, size_t num_test_nodes);
 
     // Tensor initialization
     GGML_API enum ggml_status ggml_backend_tensor_alloc(ggml_backend_buffer_t buffer, struct ggml_tensor * tensor, void * addr);