Fix OpenVINO conversion with older optimum-intel

[Sylvester Kaczmarek (sylvesterkaczmarek)]

Describe your changes

Fixes #2344.

OpenVINOOptimumConversion unconditionally imports the private _GPTOSSQuantizationConfig symbol. Versions of optimum-intel that predate that GPT-OSS helper do not expose the symbol, so an otherwise valid OpenVINO installation fails during import and Olive reports the misleading "Please install Intel® optimum[openvino]" error.

The GPT-OSS-specific type is now treated as an optional compatibility feature. On versions that provide it, existing GPT-OSS behaviour is unchanged. On older versions, normal quantization configurations continue through the standard _main_quantize path.

Tests

Adds regression coverage for both optimum-intel configurations that expose _GPTOSSQuantizationConfig and versions where the private symbol is absent.

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🟢 Approval recommended

The change is narrowly scoped to optionalizing a private import, preserves existing behavior when available, and adds targeted regression coverage for both compatibility paths.

Pull request overview

This PR improves OpenVINOOptimumConversion compatibility with older optimum-intel versions by avoiding an unconditional import of the private _GPTOSSQuantizationConfig type, preventing misleading “please install optimum[openvino]” failures during import while preserving GPT-OSS behavior when available.

Changes:

• Add _is_gptoss_quantization_config helper to detect GPT-OSS quantization config only when the private symbol exists.
• Remove the unconditional _GPTOSSQuantizationConfig import from the OpenVINO Optimum conversion path and gate _main_quantize accordingly.
• Add regression tests covering both “symbol present” and “symbol absent” scenarios.

File summaries

File	Description
olive/passes/openvino/optimum_intel.py	Makes GPT-OSS quantization type detection optional to maintain compatibility across optimum-intel versions.
test/passes/openvino/test_openvino_optimum_conversion.py	Adds regression tests verifying correct behavior when _GPTOSSQuantizationConfig is present or missing.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Lite

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