chore: add usdasm fetch helper

scripts/fetch_usdasm.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+REPO_URL="${USDASM_REPO_URL:-https://github.com/spannerisms/usdasm.git}"
+ROOT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+TARGET_DIR="${USDASM_DIR:-$ROOT_DIR/assets/asm/usdasm}"
+
+if [ -d "$TARGET_DIR/.git" ]; then
+  echo "usdasm already present at $TARGET_DIR"
+  exit 0
+fi
+
+if [ -e "$TARGET_DIR" ]; then
+  echo "Removing existing path at $TARGET_DIR"
+  rm -rf "$TARGET_DIR"
+fi
+
+mkdir -p "$(dirname "$TARGET_DIR")"
+git clone --depth 1 "$REPO_URL" "$TARGET_DIR"
+echo "usdasm fetched to $TARGET_DIR"