Make unit tests error on exceeding cumulative execution budget

[KtorZ]

We noticed that validateTxScriptsUnlimited we use for unit testing validators perform validation of scripts independently also considering budgets independently. That means while each validator could pass independently, they may exceed the maximum execution budget allowed for a transaction when considered altogether.

So we want to perform a second check on top of this function to look at the cumulative budget in case of success, and make sure it remains under the maximum execution budget. This will give us failure in unit tests sooner, instead of having to witness them through the end-to-end tests.