Add llamaTornado Java 25 single-file launcher with Metal backend support

[AdamBien]

Summary

• Replace (or complement) the Python llama-tornado launcher with llamaTornado, a zero-dependency Java 25 single-file script (#!/usr/bin/env -S java --source 25)
• Add --metal backend support for TornadoVM 4.0 on Apple Silicon
• Update README: replace deprecated OpenCL Apple Silicon note with Metal backend section and add llamaTornado usage example

Test plan

• Run ./llamaTornado --gpu --verbose-init --metal --model <model.gguf> --prompt "what is java" on Apple Silicon
• Run ./llamaTornado --gpu --opencl --model <model.gguf> --prompt "test" on NVIDIA/Intel GPU
• Verify ./llamaTornado -help and ./llamaTornado -version output
• Confirm --show-command prints the full Java invocation without executing