chore: improved mutate script so we don't end up with hunders of GBs of gremlins cache after a few slices

scripts/mutate.sh

@@ -2,7 +2,9 @@
 set -euo pipefail
 
 root="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
-work="$(mktemp -d)"
+work="$root/tmp/mutate-work"
+rm -rf "$work"
+mkdir -p "$work"
 trap 'rm -rf "$work"' EXIT
 trap 'echo "mutate: interrupted" >&2; exit 130' INT TERM