Fix five defects the port uncovered in the reference parser and scanner

Chained subtraction and exponentiation fold left instead of abandoning the
rest of the line -- `1 - 2 - 3` gave -1 and dropped the `- 3`. A unary leaf's
operand moves to .left, so a negative literal is one argument again and a
second argument no longer overwrites it. An operator in a line's final column
survives. Hex literals reach the parser whole. A leading zero is padding, not
a radix.

Item 16 stays pinned: the fix works and costs an upstream golden case, which
is a decision rather than a defect.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/runtime_commands.c

@@ -377,8 +377,8 @@ static akerr_ErrorContext *parse_line_range(akbasic_Runtime *obj, akbasic_ASTLea
     }
     if ( expr->right->leaftype == AKBASIC_LEAF_UNARY &&
 	 expr->right->operator_ == AKBASIC_TOK_MINUS ) {
-	/* -n: from the start through n. */
-	PASS(errctx, akbasic_runtime_evaluate(obj, expr->right->right, &value));
+	/* -n: from the start through n. A unary leaf's operand is on .left. */
+	PASS(errctx, akbasic_runtime_evaluate(obj, expr->right->left, &value));
 	FAIL_NONZERO_RETURN(errctx, (value->valuetype != AKBASIC_TYPE_INTEGER), AKBASIC_ERR_TYPE,
 			    "Expected a line number range");
 	*endidx = value->intval;