Integrate Wasmtime for the sandbox

[clearloop]

References

• Integrate Wasmtime for runtime execution
• Refactor the internals of Func to remove layers of indirection
• Can't mutate state from Funcs passed as wasm imports
• WebAssembly Reference Types in Wasmtime
• How to call functions where args must be passed at the stack
• The Rust Pointer Guide
• Rust Casts
• How to define extern func with referenced mutable arguments
• Rust allows &mut aliasing on static mut variables
• Relaxing static lifetime of Func::wrap arguments
• Signatures of functions are not registered in wasmtime-api crate