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

crates/oxide_emit/src/expr/identifier.rs

@@ -0,0 +1,36 @@
+use crate::{CompileCtx, Emitter};
+use oxide_ir::inst::Inst;
+use oxide_ir::operand::Operand;
+use oxide_bytecode::opcode::OpCode;
+
+impl Emitter {
+    pub(crate) fn emit_identifier_expression(
+        &self, ident: &oxide_parser::IdentifierReference, ctx: &mut CompileCtx,
+    ) -> Result<u8, String> {
+        let name = ident.name.as_str();
+
+        for (uv_idx, up) in ctx.current_upvalue_captures.iter().enumerate() {
+            if up.name == name {
+                let r = ctx.alloc_reg();
+                let idx = uv_idx as u8;
+                ctx.inst(Inst::new(OpCode::LOAD_UPVALUE, Operand::Reg(r as u32), Operand::Reg(idx as u32), Operand::None));
+                return Ok(r);
+            }
+        }
+
+        if let Some(&cell_idx) = ctx.captured_bindings.get(name) {
+            let r = ctx.alloc_reg();
+            if let Some((binding, _)) = ctx.scopes.symbols.lookup_any_binding(name) {
+                ctx.inst(Inst::new(OpCode::CELL_GET, Operand::Reg(r as u32), Operand::Reg(binding.reg as u32), Operand::Imm(cell_idx as u16)));
+            } else {
+                ctx.inst(Inst::new(OpCode::CELL_GET, Operand::Reg(r as u32), Operand::None, Operand::Imm(cell_idx as u16)));
+            }
+            return Ok(r);
+        }
+
+        let var_reg = ctx.lookup_or_builtin(name)?;
+        let r = ctx.alloc_reg();
+        ctx.inst(Inst::new(OpCode::LOAD_VAR, Operand::Reg(r as u32), Operand::Reg(var_reg as u32), Operand::None));
+        Ok(r)
+    }
+}