feat: Add base64 image support to llm_inference

Detailed description of the requested feature

The llm_inference command currently supports VLM image inputs only when the image is provided via a local file path. This prevents input files from referencing images as base64-encoded data URLs.

I would like to add support for base64-encoded images, like data:image/jpeg;base64,... or data:image/png;base64,....

This would make llm_inference easier to use across same filesystem. It would also simplify integration with evaluation frameworks such as LMMs-Eval, where images may already be available as base64-encoded data.

My work-around implementation is available at: https://github.com/FABallemand/TensorRT-Edge-LLM/tree/feat/llm_inference_base64_support

Timeline

No hard deadline.

Describe alternatives you've considered

The current workaround is to save the image to a file and update the image path in the input file. This adds unnecessary filesystem I/O.

Adding native base64 image support to llm_inference would provide a more interoperable solution while preserving the existing file-path behavior.

Target hardware/use case

Jetson Thor (SM_110, JetPack 7.1, TensorRT 10.13.3.9).

Start at the llm_inference command's VLM image-input handling and trace how input files currently resolve local image paths. Exercise it with JPEG and PNG data URLs while retaining path support; done means both forms work without requiring an intermediate image file.