epic: Cortex can detect track free and used VRAM and RAM

[dan-menlo]

Goal

• Cortex.cpp can detect total, free and used VRAM and RAM
• This is pre-requisite to avoid OOM when loading multiple models
• Pre-requisite for intelligent features (e.g. smart model unloading), e.g. Triton

Related

• epic: cortex ps and Process Status #1187
• feat: TensorRT-LLM load multiple models cortex.tensorrt-llm#33

[dan-menlo]

Closing in favor of #1165