Add error-path tests for InferenceSession Run/Load/Initialize validation

[Gopalakrishnan Nallasamy (GopalakrishnanN)]

Description

Adds error-path unit tests for InferenceSession validation / early-return branches, which were under-covered (only failure/kExpectFailure-style assertions were a small fraction of the suite). All nine target previously-untested branches and are verified passing against a local Release build.

Test	Branch exercised	Asserted message
RunBeforeInitializeReturnsError	Run when not initialized	Session not initialized
InitializeBeforeLoadReturnsError	Initialize with no model loaded	Model was not loaded
RunWithInvalidOutputNameReturnsError	ValidateOutputs unknown output	Invalid output name
RunWithWrongInputTypeReturnsError	CheckTypes (input)	Unexpected input data type
RunWithWrongInputRankReturnsError	CheckShapes (input rank)	Invalid rank for input
RunWithMismatchedFeedCountReturnsError	feed/name count mismatch	feed names has ...
RunWithWrongOutputTypeReturnsError	CheckTypes (output)	Unexpected output data type
LoadMalformedModelFromArrayReturnsError	malformed model bytes	graceful failure
LoadNonexistentModelReturnsError	missing model file	graceful failure

Motivation and Context

Error/validation paths in InferenceSession::Run / Initialize / Load were thinly tested relative to the numeric happy-path bulk. These tests lock in the failure contracts (both the non-OK Status and the message substring, via ASSERT_STATUS_NOT_OK_AND_HAS_SUBSTR) so a regression that changes the behavior or the message surfaces clearly.

Notes

• "Invalid input name" is already covered by TestOptionalInputs, so it is intentionally not duplicated.
• Test-only change (onnxruntime/test/framework/inference_session_test.cc); no product/runtime code is touched.

[Copilot]

Pull request overview

This PR strengthens ONNX Runtime’s InferenceSession unit test coverage by adding targeted tests for validation and early-return error paths in Load, Initialize, and Run, ensuring these failure contracts (Status + message substrings) are guarded against regressions.

Changes:

• Add new unit tests covering Run before Initialize, Initialize before Load, and invalid output-name validation.
• Add new unit tests covering input/output type and shape validation failures, plus feed-name/value count mismatch.
• Add new unit tests ensuring malformed model bytes and nonexistent model paths fail gracefully.