Apply rustfmt and reduce chunk harness MAX_LEN to fix CI timeouts

- Apply upstream rustfmt formatting via check_rustc.sh --bless
- Reduce MAX_LEN for u8 and () chunk harnesses from u32::MAX/isize::MAX
  to 128 to prevent CBMC autoharness and partition timeouts. The
  verification value comes from proving correctness for arbitrary-length
  slices up to the bound, not from the absolute size.

Author: jrey8343