fix: pin torch/torchaudio to 2.5.1 (CUDA 12 compatible)

The unpinned >=2.0.0 was resolving to torch 2.9+ which links against
libcudart.so.13 (CUDA 13). HF Space base image only ships CUDA 12, so
import torchaudio failed with 'libcudart.so.13: cannot open shared
object file'. Pin to 2.5.1 which uses cu121 wheels.

requirements.txt

@@ -1,7 +1,7 @@
 https://github.com/CPJKU/beat_this/archive/main.zip
 gradio>=4.0.0
-torch>=2.0.0
-torchaudio>=2.0.0
+torch==2.5.1
+torchaudio==2.5.1
 pytorch-lightning>=2.0.0
 transformers>=4.46.0
 huggingface_hub>=0.25.0,<1.0.0