Bound TreeEnsemble subtree comparison (#32043)
This pull request improves the robustness and correctness of categorical
node folding in the tree ensemble implementation by refactoring the
subtree comparison logic to prevent infinite loops caused by cycles, and
by adding a test to ensure cycles are properly detected and rejected.
**Categorical Node Folding and Cycle Detection Improvements:**
* Refactored the `CheckIfSubtreesAreEqual` method in
`tree_ensemble_common.h` to use an iterative approach with explicit
cycle detection, replacing the previous recursive implementation. This
prevents stack overflows and infinite loops when cycles are present in
the tree structure.
(`onnxruntime/core/providers/cpu/ml/tree_ensemble_common.h`,
[[1]](diffhunk://#diff-098f04f4ce424d09171371b1dc5893d29e38c42a0f880639775de9e0fec67241L115-R116)
[[2]](diffhunk://#diff-098f04f4ce424d09171371b1dc5893d29e38c42a0f880639775de9e0fec67241L411-R462)
* Modified the categorical node folding logic in `AddNodes` to maintain
a set of visited categorical nodes and enforce that no node is
revisited, raising an error if a cycle is detected.
(`onnxruntime/core/providers/cpu/ml/tree_ensemble_common.h`,
[onnxruntime/core/providers/cpu/ml/tree_ensemble_common.hR537-R544](diffhunk://#diff-098f04f4ce424d09171371b1dc5893d29e38c42a0f880639775de9e0fec67241R537-R544))
* Added `#include <set>` to support the new cycle detection logic.
(`onnxruntime/core/providers/cpu/ml/tree_ensemble_common.h`,
[onnxruntime/core/providers/cpu/ml/tree_ensemble_common.hR8](diffhunk://#diff-098f04f4ce424d09171371b1dc5893d29e38c42a0f880639775de9e0fec67241R8))
**Testing:**
* Added a new unit test `TreeRegressorRejectsCategoricalCycle` to verify
that the implementation correctly detects and rejects cycles in
categorical nodes, ensuring the model fails gracefully with an
appropriate error message.
(`onnxruntime/test/providers/cpu/ml/treeregressor_test.cc`,
[onnxruntime/test/providers/cpu/ml/treeregressor_test.ccR768-R789](diffhunk://#diff-08b3495816c68f145657ecff63d7b5f3d56813586ec62f7324c22977e70e336bR768-R789))
