Implement Phase 1: MIR + VM backend with golden tests

Co-authored-by: moe-charm <217100418+moe-charm@users.noreply.github.com>

src/backend/mod.rs

@@ -0,0 +1,7 @@
+/*!
+ * Backend module - Different execution backends for MIR
+ */
+
+pub mod vm;
+
+pub use vm::{VM, VMError};