[QNN EP] Dump UT artifacts for debugging

[yuhuchua-qti]

Description

This change introduces new environment variables to make debugging failed unit tests easier by saving input/output artifacts:

• ORT_UNIT_TEST_DUMP_ARTIFACTS: Dumps inputs, outputs, and expected outputs for test cases.
• ORT_UNIT_TEST_ARTIFACTS_DIR: Sets the directory where artifacts are stored. Defaults to the current working directory if not provided.

Examples

Example 1: Using ORT_UNIT_TEST_DUMP_ARTIFACTS
PowerShell: $Env:ORT_UNIT_TEST_DUMP_ARTIFACTS = "1";

C:.
├───QnnCPUBackendTests_DISABLED_Gemm_Broadcast_Bias_DynamicA_StaticB_DynamicC  # TestModelAccuracy 
│   ├───CPU_EP_outputs
│   │       output.pb
│   │
│   ├───inputs
│   │       input.pb
│   │       input_token_0.pb
│   │
│   └───QNNExecutionProvider_outputs
│           output.pb
│
└───QnnHTPBackendTests_DISABLED_BinaryOp_Div4D_LargeInputs  # TestQDQModelAccuracy 
    ├───CPU_EP_F32_outputs
    │       output.pb
    │
    ├───CPU_EP_QDQ_outputs
    │       output.pb
    │
    ├───inputs
    │       input.pb
    │       input_token_5.pb
    │
    └───QNN_EP_QDQ_outputs
            output.pb