Fix Pallas GPU lowering by using Triton backend

JAX 0.10.1 defaults to Mosaic GPU backend which fails due to missing
absl-py. Set JAX_PALLAS_USE_MOSAIC_GPU=0 to use Triton backend and
install absl-py for future Mosaic GPU compatibility.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Tyronita

.github/workflows/gpu-benchmark.yml

@@ -27,6 +27,7 @@ env:
   BENCH_SIZE: ${{ inputs.size || 'MEDIUM' }}
   BENCH_LEVELS: ${{ inputs.levels || '1 2 3' }}
   BENCH_ALERT: ${{ inputs.alert_threshold || '150' }}
+  JAX_PALLAS_USE_MOSAIC_GPU: "0"
 
 jobs:
   benchmark:
@@ -43,6 +44,7 @@ jobs:
 
       - name: Install JAX (CUDA)
         run: |
+          pip install absl-py
           pip install -e ".[gpu,dev]"
 
       - name: Verify GPU