feat(cheatcodes): getBlockNumber and getBlockTimestamp

[Evalir]

Motivation

Closes #6180

[mattsse]

Ah right, this acts like a blockbox so the compiler doesn't inline it.

can we add a note to the docs about this?

[ZeroEkkusu]

Just a heads up that this is not documented in a visible place, yet can result in false passing tests.
It needs to be documented in warp, skip, rewind, and any other places where the block timestamp/number is changed.