LEVM: Refactor the main method flow

[ilitteri]

• The new transact method should: prepare the VM for execution -> execute -> resolve the execution result -> perform the post-execution logic -> return the transaction execution report.
• execute should return an ExecutionResult.
• There should be a resolve_execution_result function that takes the ExecutionResult and returns the TransactionExecutionReport.
• The TransactionExecutionReport should be altered by the post-execution logic as needed.