Add diagnostic context to ORT_ENFORCE bounds checks in TreeEnsemble operators

[Copilot]

Description

Adds informative error messages to the three ORT_ENFORCE index-bounds checks in tree_ensemble_common.h that validate target_class_ids, target_class_weights, and target_class_weights_as_tensor accesses. Each message now surfaces the failing index i and the container size, e.g.:

Index i=5 is out of bounds for target_class_ids (size=3)
Index i=5 is out of bounds for target_class_weights (size=3)
Index i=5 is out of bounds for target_class_weights_as_tensor (size=3)

Motivation and Context

The original bare ORT_ENFORCE(i < ...) calls produced opaque failures with no indication of which attribute was malformed or what the actual index/size values were. This made it difficult to diagnose invalid or adversarial models. Addresses feedback from #27677.

---

🔒 GitHub Advanced Security automatically protects Copilot coding agent pull requests. You can protect all pull requests by enabling Advanced Security for your repositories. Learn more about Advanced Security.