Add support for quantized qwen2-0.5b

[bil-ash]

Add support for quantized(q4f16) qwen2-0.5b . Wasm library taken from https://huggingface.co/julientfai/Qwen2-0.5B-Instruct-q4f16_1-Opilot/resolve/main/Qwen2-0.5B-Instruct-q4f16_1-webgpu.wasm?download=true

[Neet-Nestor]

Related PRs:

• https://github.com/mlc-ai/web-llm/pull/490
• https://github.com/mlc-ai/web-llm-chat/pull/44
• https://github.com/mlc-ai/binary-mlc-llm-libs/pull/128

[bil-ash]

I have renamed as suggested. By the way, what is prefill chunk size and how does it relate to memory usage and performance?

[CharlieFRuan]

Thanks! Say prefill chunk size is 2k, if a prompt is 4k, it will be prefilled twice instead of all at once. This helps reduce the size of the intermediate buffer for the matrix multiplication.