Clean build environment before each bisect step (PR-55)

Summary:
Add build environment cleanup before building Triton to ensure a clean
state for each bisect step. This prevents stale artifacts and package
conflicts from affecting bisect results.

Changes:
1. Clean build directories
   - Remove $TRITON_DIR/build (compiled artifacts)
   - Remove $TRITON_DIR/python/triton.egg-info (package metadata)

2. Uninstall existing triton packages
   - Remove 'triton' and 'pytorch-triton' packages before build
   - Prevents conflicts with PyTorch built-in triton
   - Supports both pip and uv (USE_UV=1)

This ensures each bisect step starts with a clean build environment,
preventing issues where:
- Incremental builds fail due to stale artifacts
- Old triton versions interfere with newly built versions
- PyTorch's built-in triton causes version conflicts

Reviewed By: wychi

Differential Revision: D91072543

fbshipit-source-id: b5ba62a316a6a223f7a75aba69c01080d832e226

Author: FindHao

tritonparse/bisect/scripts/bisect_triton.sh

@@ -182,6 +182,21 @@ fi
 
 echo "" | log_output
 
+# Clean build directory to avoid stale artifacts from previous commits
+echo "Cleaning build directory..." | log_output
+rm -rf "$TRITON_DIR/build"
+rm -rf "$TRITON_DIR/python/triton.egg-info"
+echo "" | log_output
+
+# Uninstall any existing triton to avoid conflicts with PyTorch built-in
+echo "Uninstalling existing triton packages..." | log_output
+if [[ "$USE_UV" == "1" ]]; then
+  uv pip uninstall -y triton pytorch-triton 2>&1 | log_output || true
+else
+  pip uninstall -y triton pytorch-triton 2>&1 | log_output || true
+fi
+echo "" | log_output
+
 # Build Triton
 echo "Building Triton..." | log_output
 BUILD_START=$(date +%s)