Package `@aztec/simulator` contained a weird amalgamation of a generic
"circuit simulator" (that could execute kernels, which are mostly
vanilla noir circuits) and a very specific "aztec simulator" that
executed aztec contract functions with a very particular set of oracles
always provided by PXE. This caused a weird split, since both packages
usually have to be edited at the same time as they're tightly coupled.

This PR tries to remove most of Aztec's specific stuff into PXE, to what
we call the `ContractFunctionSimulator` for private, leaving `simulator`
only as a thin abstraction on top of the `acvm` with extra niceties,
such as oracle recording capabilities and error decoding.