fix: use block comments in CR mutator to prevent compilation errors

[stevennevins]

Summary

CR mutator now uses block comments (/* */) instead of line comments (//).

Problem

Line comment // comments out everything after it on the line. This breaks compilation when code continues:

// Original
function test() public onlyOwner {

// With // - BROKEN
function test() public // onlyOwner {

// With /* */ - WORKS  
function test() public /* onlyOwner */ {

Solution

new_str = "/* " + old_str + " */"

Scenarios Improved

Function modifier same line as brace:

// Original
function foo() onlyOwner {

// Before (broken)
function foo() // onlyOwner {

// After (works)
function foo() /* onlyOwner */ {

Single-line functions:

// Original
function getX() view returns (uint) { return x; }

// Before (broken) - commenting return statement
function getX() view returns (uint) { // return x; }

// After (works)
function getX() view returns (uint) { /* return x; */ }