Bump torch 2.4.0 -> 2.8.0 for ZeroGPU compat

ZeroGPU validator was silently tightened (now requires torch >= 2.8.0; 2.4.0 dropped). Also pins xformers==0.0.32.post2 (canonical torch-2.8 build with sm_90 wheels) and bumps bitsandbytes floor to 0.45.0.

requirements.txt

@@ -1,5 +1,5 @@
-torch==2.4.0
-torchaudio==2.4.0
+torch==2.8.0
+torchaudio==2.8.0
 # pydantic 2.11+ emits bool-shorthand `additionalProperties: True` which crashes
 # gradio_client's get_type (`if "const" in schema`). 2.10.6 is the last version
 # that still emits the dict form. Tracked at:
@@ -8,14 +8,14 @@ pydantic==2.10.6
 safetensors>=0.4.0
 accelerate>=0.25.0
 peft>=0.7.0
-xformers>=0.0.23
+xformers==0.0.32.post2
 av>=12.0.0
 einops>=0.7.0
 PyYAML>=6.0
 sentencepiece>=0.1.99
 transformers>=4.45.0
 huggingface_hub>=0.20.0,<1.0
-bitsandbytes>=0.43.0
+bitsandbytes>=0.45.0
 gradio==5.7.1
 spaces>=0.30.0
 soundfile>=0.12.0