Move Allocator up to laythe_vm

[jonnyboyC]

Summary

I keep running into issue where new GC bugs pop up as I progress through these refactors. In general I'd like to be able to run cargo test in ci with the gc_stress on to gc on every allocation to minimize the chance of introducing one of these bugs.

Overall I think to achieve this I need to do something along the lines of thing

• Move the current allocator to laythe_vm crate
• Implement a new dummy allocator in laythe_core. Likely we can just have it never GC to simplify the implementation
• Route essentially all current allocator call through GcHooks to simplify the interface where we can have a test context that uses our dummy allocator
• Move the crate feature up to laythe_vm so we can have it be a feature when we call cargo test