feat: 字节码VM基础设施 — 编译器、VM执行循环、Runtime trait

Phase 1-3: 基础VM架构
- 新增 Runtime trait: 抽象树遍历解释器和VM的共同接口
- NativeFn 改为接受 &mut dyn Runtime
- 重构所有内置函数使用新签名
- vm/opcode.rs: 33个字节码指令 + 编码/解码辅助函数
- vm/compiler.rs: AST→字节码编译器，支持变量解析、跳转回填、作用域
- vm/vm.rs: 栈式VM执行循环，支持全局变量、原生函数调用
- lib.rs: 新增 run_file_vm() + --vm CLI标志
- 修复: 跳转偏移计算、对象字面量编译

工作特性: 算术、变量、while/for循环、条件、数组、对象、字符串
待完成: 用户定义函数调用、闭包/upvalue捕获、完整require支持

Release模式: 1M算术循环 VM 0.44s vs 树遍历 0.89s (2.0x加速)

aster-core/src/interpreter/mod.rs

@@ -13,7 +13,16 @@ use std::rc::Rc;
 use std::cell::RefCell;
 use std::fmt;
 
-pub type NativeFn = Rc<dyn Fn(&mut super::Interpreter, Vec<Value>) -> Result<Value, crate::error::RuntimeError>>;
+/// Trait abstracting runtime services that native functions may need.
+/// Both the tree-walking `Interpreter` and the bytecode `Vm` implement this.
+pub trait Runtime {
+    /// Load and execute a module, returning its exports object.
+    /// Implementations differ: tree-walker interprets directly,
+    /// VM compiles to bytecode then executes.
+    fn require(&mut self, path: &str) -> Result<Value, crate::error::RuntimeError>;
+}
+
+pub type NativeFn = Rc<dyn Fn(&mut dyn Runtime, Vec<Value>) -> Result<Value, crate::error::RuntimeError>>;
 
 #[derive(Clone)]
 pub enum Value {