String equality (==/!=) already worked, but the relational operators
(<, <=, >, >=) rejected string operands (typed mismatch).
Enhancement-106 makes them perform a lexicographic comparison (via strcmp),
completing the string comparison surface.
stringcmp_demo.va evaluates "abc" < "abd" (=1), "abd" > "abc" (=1),
"abc" <= "abc" (=1), "abc" >= "abd" (=0), "abc" < "abc" (=0),
"abc" == "abc" (=1, equality still works), and uses a string relational as an
if condition ("high" < "low" → true). Run: python3 verify_stringcmp.py
(8 checks).