Extend the list subscript operator to accept Range arguments in addition to plain numbers. When a Range is provided, the operator returns a new list containing the elements within that range, supporting inclusive (..) and exclusive (...) bounds, negative indices that count from the end, and automatic reversal for backwards ranges. Added validation functions for integer values and range bounds, with dedicated error messages for non-integer range endpoints and out-of-bounds conditions. Updated the test suite with comprehensive range subscript tests and removed the old test that only checked for non-numeric subscripts.
Bob Nystrom
Kyle Marek-Spartz