feat(soroban): Add support for storage vectors

[salaheldinsoliman]

Storage vectors here are not supported via keeping a VecObject in storage.
Instead, we follow an approach similar to how storage vectors in Solidity: The key is a hash function of (storage slot + index). This hash function in Soroban is simply a VecObject :)

contract storage_array {
            uint64[] mylist;
            uint64 normal = 20;

            function push_pop() public returns (uint64) {
                mylist.push(5);
                mylist[0] = 15;
                return mylist[0] ;
            }
  }

Here mylist[0] element is addressed as VecObject(main slot + index), which in this case is VecObject(0,0)