[MultiModal] Unable to Disable OCOS_ENABLE_VENDOR_IMAGE_CODECS in ORT-GenAI Build

The build preset for ORT-GenAI [forcibly enables](https://github.com/microsoft/onnxruntime-extensions/blob/main/cmake/presets/ort_genai.cmake#L8) the option OCOS_ENABLE_VENDOR_IMAGE_CODECS=ON, and attempts to override it via OCOS_ENABLE_VENDOR_IMAGE_CODECS=OFF in the build command are ignored.

For Chromium-Sandbox use cases, it's critical to disable this flag to ensure full isolation from OS-level image codec dependencies. This limitation blocks integration of multimodal capabilities in Chromium-based browsers such as Microsoft Edge, where sandboxing and platform independence are required.

**Suggested Fix**: Allow OCOS_ENABLE_VENDOR_IMAGE_CODECS to be overridden via build command or expose a configurable toggle in the CMake presets.

Start with cmake/presets/ort_genai.cmake at line 8 and inspect how OCOS_ENABLE_VENDOR_IMAGE_CODECS is set in the ORT-GenAI build preset. Reproduce the build with OCOS_ENABLE_VENDOR_IMAGE_CODECS=OFF, then verify that the command-line override or an exposed preset toggle disables the option.

Written by the indexing model from the issue text.