refactor: 拆分 oxide_emit 为独立 emit pass crate（依赖倒置）

crates/oxide_emit/src/stmt/basic/mod.rs

@@ -0,0 +1,18 @@
+use crate::{CompileCtx, Emitter};
+use oxide_parser::Statement;
+
+mod break_continue;
+mod expression;
+mod labeled;
+mod return_stmt;
+
+impl Emitter {
+    pub(crate) fn emit_basic_domain(&self, stmt: &Statement, ctx: &mut CompileCtx) -> Result<Option<u8>, String> {
+        match stmt {
+            Statement::ExpressionStatement(_) => self.emit_basic_expression(stmt, ctx),
+            Statement::ReturnStatement(_) => self.emit_basic_return(stmt, ctx),
+            Statement::EmptyStatement(_) => Ok(None),
+            _ => Ok(None),
+        }
+    }
+}