Improve checks in concat_slice_elimination against optional attrs and unsqueeze_elimination against invalid model

[yuslepukhin]

This pull request introduces improvements to the concat_slice_elimination and unsqueeze_elimination optimizer passes, focusing on correctness, robustness, and code clarity. The changes include enhanced handling of optional Slice operator attributes, stricter validation of axes and steps, and improved error handling for invalid model inputs.

Improvements to concat_slice_elimination:

• Materialized default values for optional axes and steps in the Slice operator, ensuring safe indexing and alignment with ONNX defaults. (onnxruntime/core/optimizer/concat_slice_elimination.cc)
• Refined the fusion pattern to only allow starts.size() == 1, clarifying the scope of the optimization and preventing incorrect fusions. (onnxruntime/core/optimizer/concat_slice_elimination.cc)
• Added <numeric> include to support new code using std::iota. (onnxruntime/core/optimizer/concat_slice_elimination.cc)

Improvements to unsqueeze_elimination:

• Added validation for axes values, including range checks and detection of duplicate axes, returning errors for invalid models instead of silently proceeding. (onnxruntime/core/optimizer/unsqueeze_elimination.cc)
• Added core/providers/common.h include for utility functions used in validation. (onnxruntime/core/optimizer/unsqueeze_elimination.cc)

[Copilot]

Pull request overview

Improves robustness and correctness of two optimizer passes (ConcatSliceElimination and UnsqueezeElimination) by adding safer handling of optional Slice inputs and stricter validation of Unsqueeze axes, and extends the optimizer unit test suite to cover these scenarios.

Changes:

• Materialize default axes/steps for Slice in ConcatSliceElimination and tighten the supported fusion pattern to starts.size() == 1.
• Add out-of-range and duplicate-axis validation to UnsqueezeElimination, returning explicit errors for invalid models.
• Add targeted optimizer tests for Unsqueeze elimination and Slice optional-input defaulting behavior.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
onnxruntime/test/optimizer/graph_transform_test.cc	Adds unit tests for Unsqueeze elimination behavior and for Concat+Slice fusion when Slice omits optional axes/steps.
onnxruntime/core/optimizer/unsqueeze_elimination.cc	Adds axis range/dup validation for Unsqueeze elimination and improves robustness against invalid models.
onnxruntime/core/optimizer/concat_slice_elimination.cc	Materializes Slice default axes/steps, adds <numeric>, and narrows fusion eligibility to single-dimension slicing.

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[yuslepukhin]

/azp run Linux TensorRT CI

[azure-pipelines]

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