Remove code duplication between Cairo Native and Sierra Emu

[JulianGCalderon]

Right know, both Cairo Native and Sierra Emu share some utility functions and definitions. See, for example:

• Native's debug.rs vs. Emu's debug.rs

• Native's SyscallHandler vs. Emu's SyscallHandler.

NOTE: There may be more duplicated code than what is mentioned here.

We should figure a way of removing this duplication. I can think of two alternatives:

• Have Sierra Emu depend on Cairo Native, and move this utilities/definitions to Native. Right know, Cairo Native depends on SIerra Emu.

• Move the shared logic to an auxiliary crate.