Override load_elf and load_binary for DefaultCoreMachine and DefaultMachine.

[mohanson]

• Override DefaultCoreMachine's load_binary so when pprof is enabled, the original code can be saved.
• Override DefaultMachine's load_binary and load_elf. It now calls inner's related methods by default.

The purpose of these changes is to get the original code from the machine created by the spawn scheduler.

[xxuejie]

I have no objections to this so I will just approve it. Though I wonder if we can split pprof related code out of the core crate into its own thing.

[mohanson]

I will try to remove the pprof feature from ckb-vm. But for now, this is the easiest way to help ckb-debugger get the original code.