message: Add a debug-assert to check allocation sizing
  Summary: If I have an off-by-one in the capacity calculation it will cause excess memory allocation. To ensure I don't, add a debug assertion.
diff: @@ -952,6 +952,7 @@ pub(crate) fn string_methods(builder: &mut GlobalsBuilder) {
  .split(|x| *x == b)
  .map(|x| heap.alloc(unsafe { std::str::from_utf8_unchecked(x) })),
  );
  + debug_assert_eq!(res.len(), count + 1);
  res
  } else {
  this.split(sep).map(|x| heap.alloc(x)).collect()
  