fix: avoid vector copies in CheckIfSubtreesAreEqual (microsoft#27854)

`indices` is built once and then only read during recursive calls to
`CheckIfSubtreesAreEqual`. However it was passed by value, causing a
full copy on every recursive call. Changed to `const&`.

## Data from the profiler:
To collect the following data, a model with a single
TreeEnsembleClassifier node (5000 trees and 3.3 million nodes) has been
used. The loading time dropped from 18 minutes to about 4 seconds.

### After
<img width="1793" height="547" alt="Screenshot 2026-03-25 at 6 40 25 PM"
src="https://github.com/user-attachments/assets/d7c00335-8246-4bd1-9e4d-b0e956d48cdd"
/>


### Before
<img width="1763" height="548" alt="Screenshot 2026-03-25 at 6 40 40 PM"
src="https://github.com/user-attachments/assets/35683112-2919-4031-955c-922937f2df8f"
/>

Author: lhrios

onnxruntime/core/providers/cpu/ml/tree_ensemble_common.h

@@ -115,7 +115,7 @@ class TreeEnsembleCommon : public TreeEnsembleCommonAttributes {
                                const InlinedVector<size_t>& truenode_ids, const InlinedVector<size_t>& falsenode_ids, gsl::span<const int64_t> nodes_featureids,
                                gsl::span<const ThresholdType> nodes_values_as_tensor, gsl::span<const float> node_values,
                                gsl::span<const float> target_class_weights, gsl::span<const ThresholdType> target_class_weights_as_tensor,
-                               const InlinedVector<TreeNodeElementId>& node_tree_ids, InlinedVector<std::pair<TreeNodeElementId, uint32_t>> indices);
+                               const InlinedVector<TreeNodeElementId>& node_tree_ids, const InlinedVector<std::pair<TreeNodeElementId, uint32_t>>& indices);
   size_t AddNodes(const size_t i, const InlinedVector<NODE_MODE_ONNX>& cmodes, const InlinedVector<size_t>& truenode_ids,
                   const InlinedVector<size_t>& falsenode_ids, gsl::span<const int64_t> nodes_featureids,
                   gsl::span<const ThresholdType> nodes_values_as_tensor, gsl::span<const float> node_values,
@@ -383,7 +383,7 @@ bool TreeEnsembleCommon<InputType, ThresholdType, OutputType>::CheckIfSubtreesAr
     const InlinedVector<size_t>& truenode_ids, const InlinedVector<size_t>& falsenode_ids, gsl::span<const int64_t> nodes_featureids,
     gsl::span<const ThresholdType> nodes_values_as_tensor, gsl::span<const float> node_values,
     gsl::span<const float> target_class_weights, gsl::span<const ThresholdType> target_class_weights_as_tensor,
-    const InlinedVector<TreeNodeElementId>& node_tree_ids, InlinedVector<std::pair<TreeNodeElementId, uint32_t>> indices) {
+    const InlinedVector<TreeNodeElementId>& node_tree_ids, const InlinedVector<std::pair<TreeNodeElementId, uint32_t>>& indices) {
   if (left_id == right_id) {
     return true;
   }