(js-div 1 0) with rational integer literals throws "rational: division
by zero" instead of producing Infinity. Wrapped the divisor in
(exact->inexact ...) so integer-by-zero now returns inf/-inf/nan
matching JS semantics. Hit by the harness's _isSameValue +0/-0 check
which calls (js-div 1 a) on JS literal arguments.
built-ins/Number: 37/50 → 41/50. built-ins/String: 77/99.
conformance.sh: 148/148.