Harden contrib CPU int narrowing for attention attrs

[apsonawane]

This pull request strengthens input validation for attention-related operators and adds corresponding unit tests to ensure that large attribute values do not cause integer overflows. The changes affect the LinearAttention, LongformerAttentionBase, and GPT subgraph implementations, improving reliability and error reporting.

Input validation improvements:

• onnxruntime/contrib_ops/cpu/bert/linear_attention.cc: Added checks to ensure q_num_heads and kv_num_heads attributes are within the range [1, INT_MAX], preventing integer overflows during initialization.
• onnxruntime/contrib_ops/cpu/bert/longformer_attention_base.h: Added validation to ensure num_heads and window attributes are within [1, INT_MAX].
• onnxruntime/contrib_ops/cpu/transformers/subgraph_gpt.cc: Added checks to ensure certain tensor dimensions do not exceed INT_MAX, preventing unsafe casts.

Testing enhancements:

• onnxruntime/test/contrib_ops/linear_attention_op_test.cc: Added new tests to verify that the LinearAttention operator correctly rejects out-of-range q_num_heads and kv_num_heads values, ensuring the new validation logic is exercised.

Code maintenance:

• Included <limits> header where necessary to support the new validation checks. [1] [2] [3]

[Copilot]

Pull request overview

This PR hardens contrib CPU attention-related operators against unsafe int64_t→int narrowing by validating attribute/tensor-dimension ranges and adds unit tests to ensure overflow-scale values are rejected with clear errors.

Changes:

• Add INT_MAX-bounded validation for q_num_heads/kv_num_heads (LinearAttention) and num_heads/window (LongformerAttentionBase) before static_cast<int>().
• Add INT_MAX-bounded validation for GPT subgraph dimension values before narrowing to int.
• Add LinearAttention unit tests that exercise the new overflow-range validation for head-count attributes.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
onnxruntime/contrib_ops/cpu/bert/linear_attention.cc	Validates q_num_heads/kv_num_heads are within [1, INT_MAX] prior to narrowing to int.
onnxruntime/contrib_ops/cpu/bert/longformer_attention_base.h	Validates num_heads and window are within [1, INT_MAX] prior to narrowing to int.
onnxruntime/contrib_ops/cpu/transformers/subgraph_gpt.cc	Validates key subgraph shape dims are <= INT_MAX before narrowing to int.
onnxruntime/test/contrib_ops/linear_attention_op_test.cc	Adds failure-mode tests for out-of-range q_num_heads/kv_num_heads.