Function nat_lex_cmp 

pub fn nat_lex_cmp(a: &str, b: &str) -> Ordering

A hybrid comparator for string slices:

• If the two strings have the same length, performs a standard lexicographical (byte-wise) comparison.
• Otherwise, falls back to a natural order comparison (natord::compare).

This is useful for sorting lists containing both fixed-length identifiers (like ULIDs) and variable-length names with embedded numbers (like filenames).

Arguments

• a: The first string slice.
• b: The second string slice.

Returns

An Ordering indicating whether a is less than, equal to, or greater than b.