[Kernel] Fix einsum operator for empty inputs

[hariharans29]

Description

Dupe of #23379 - opening new PR to debug pending build issues before merging

Motivation and Context

Fix Einsum handling of empty inputs
Bug identification credit: @neNasko1

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Pull request overview

This pull request fixes a segmentation fault in the einsum operator when handling empty input tensors. The fix implements an early return path that detects empty inputs and zero-fills the output tensor, avoiding the crash that occurred when the main computation path attempted to process empty tensors.

Changes:

• Added Zeroing device helper functions for CPU and CUDA providers to zero-fill tensor buffers
• Implemented empty input detection logic in the einsum compute processor
• Added 5 comprehensive test cases covering various empty input scenarios (outer product, transpose, vanishing dimensions in 2D and 3D)

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
onnxruntime/test/providers/cpu/math/einsum_test.cc	Added 5 test cases for empty input scenarios with expected outputs
onnxruntime/core/providers/cpu/math/einsum_utils/einsum_auxiliary_ops.h	Added Zeroing function declaration for CPU provider
onnxruntime/core/providers/cpu/math/einsum_utils/einsum_auxiliary_ops.cc	Implemented CPU Zeroing function using memset
onnxruntime/core/providers/cuda/math/einsum_utils/einsum_auxiliary_ops.h	Added Zeroing function declaration for CUDA provider
onnxruntime/core/providers/cuda/math/einsum_utils/einsum_auxiliary_ops.cc	Implemented CUDA Zeroing function using cudaMemsetAsync
onnxruntime/core/providers/cpu/math/einsum_utils/einsum_typed_compute_processor.h	Added zero_input_buffer_func_ member and updated SetDeviceHelpers signature
onnxruntime/core/providers/cpu/math/einsum_utils/einsum_typed_compute_processor.cc	Implemented empty input detection and early return logic
onnxruntime/core/providers/cpu/math/einsum.cc	Updated SetDeviceHelpers calls to include Zeroing function
onnxruntime/core/providers/cuda/math/einsum.cc	Updated SetDeviceHelpers calls to include Zeroing function
onnxruntime/core/providers/cpu/cpu_provider_shared.h	Updated shared provider interface with Zeroing parameter
onnxruntime/core/providers/cpu/cpu_provider_shared.cc	Updated shared provider implementation with Zeroing parameter

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