feat: add ACE-Step-1.5 support

[rmatif]

This PR add initial support for ACE-Step-1.5

CLI eg:

PROMPT="$(cat prompt.txt)"; LYRICS="$(cat lyrics.txt)";
./build/bin/sd-cli \
  -M audio_gen \
  -m /models/ace_step_1.5_turbo_aio.safetensors \
  -p "$PROMPT" \
  --lyrics "$LYRICS" \
  --sampling-method euler --scheduler simple --cfg-scale 1 --flow-shift 3 --steps 8 \
  --duration 120 --timesignature 4 \
  --language en --keyscale "G major" --bpm 120 \
  --lm-seed 32 -s 32 --fa \
  -o output.wav

Generates 120s of audio in under 12s on an RTX 4090

Download the model: https://huggingface.co/Comfy-Org/ace_step_1.5_ComfyUI_files/blob/main/checkpoints/ace_step_1.5_turbo_aio.safetensors

Required ggml submodule for now: https://github.com/rmatif/ggml/tree/ace

Since this is a text-to-music model and it introduces significant changes and new code, I’m wondering whether it’s preferable to integrate it into stable-diffusion.cpp, or if it would be better for me to create a separate repo (e.g ace.cpp) dedicated to this. @leejet any thoughts?

Output example:

output.mp4