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

crates/oxide_emit/src/stmt/iteration/while_loop.rs

@@ -0,0 +1,24 @@
+use crate::{CompileCtx, Emitter};
+use oxide_ir::inst::Inst;
+use oxide_parser::Statement;
+
+impl Emitter {
+    pub(crate) fn emit_while_statement(&self, stmt: &Statement, ctx: &mut CompileCtx) -> Result<Option<u8>, String> {
+        let Statement::WhileStatement(wh) = stmt else {
+            return Ok(None);
+        };
+        let start_label = ctx.next_label_id();
+        let end_label = ctx.next_label_id();
+        ctx.labels.set_label_pos(start_label, ctx.insts.len());
+        ctx.push_loop(end_label, start_label);
+        let n_labeled = ctx.take_pending_loop_labels(end_label, start_label);
+        let test_reg = self.emit_expression(&wh.test, ctx)?;
+        ctx.inst(Inst::jmp_if_false(test_reg, end_label));
+        self.emit_statement(&wh.body, ctx)?;
+        ctx.inst(Inst::jmp(start_label));
+        ctx.labels.set_label_pos(end_label, ctx.insts.len());
+        ctx.pop_label_scopes(n_labeled);
+        ctx.pop_loop();
+        Ok(None)
+    }
+}