Validating transaction operations which has contract from proposed ballot

Each node has to validate the transaction from a ballot and `stateRoot` from this ballot.
So every node executes the contract codes in transaction's operation and makes a `stateRoot` as the result.
And If it is ok, every node will change the states from this ballot's transactions and will make a block.

The issue names no files, tests, or entry points to start from. First identify where ballot transactions, contract execution, and stateRoot validation are implemented, then clarify the expected validation flow and what stateRoot and block outcomes should be tested.

Written by the indexing model from the issue text.