Measure gas usage in tests

[ya7on]

For future gas usage optimization, it needs to be measured first.
In @ton/test-utils there is totalFees parameter of transaction structure. I believe we could rely on this value for measuring gas usage. Or maybe some research is needed here to find out how to count it.
I suggest add to tests gas usage variable with predefined measured value. And substract totalFees from it (or anything else more correct if we find it)
After that issue we could start to somehow optimize gas usage.