chore: add clean.sh to remove test artifacts

clean.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+# remove-diff-out.sh
+#
+# Removes all files (including hidden) in any <pkg>/tests/<test>/diff or out directories.
+
+set -euo pipefail
+
+# 1) Make the shell match hidden files (dotfiles) in globs.
+# 2) Let an empty glob expand to zero arguments rather than itself.
+shopt -s dotglob nullglob
+
+# 2) Loop over any matching directories: <pkg>/tests/<test>/{diff,out}
+for dir in */tests/*/{diff,out}; do
+  # Only proceed if it's actually a directory
+  if [[ -d "$dir" ]]; then
+    echo "Removing files under: $dir"
+    # Remove everything inside (including hidden files)
+    rm -rf -- "$dir"/*
+  fi
+done
+
+echo "Done!"