Changing pkg structure from everything inside the vm pkg into three different ones:

1. runner: initializes the vm and executes it. A separate package since it is optional. Anyone can implement their own runner to interact with the vm.
2. program: logic that parses a casm file and turns into a Program (which is used by our runner, not vm). It may go inside the runner pkg, but I am not sure, maybe we want multiple program parsers (for example sierra-compile and starknet-sierra-compile produce different outputs)
3. vm: the reason for this project