JIT lower/builder リファクタリング: モジュール分割による整理

## 🔧 builder.rs のモジュール分割
- noop.rs: NoopBuilder実装を独立モジュールへ
- object.rs: ObjectBuilderの実装を分離
- rt_shims.rs: ランタイムシムパス関連を整理

## 目的
- 2000行超のbuilder.rsを責務単位で分割
- 可読性とメンテナンス性の向上
- 各ビルダー実装の独立性を確保

ChatGPT5による大規模リファクタリング作業の一環

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/jit/lower/builder/noop.rs

@@ -0,0 +1,34 @@
+use super::{IRBuilder, BinOpKind, CmpKind, ParamKind};
+
+pub struct NoopBuilder {
+    pub consts: usize,
+    pub binops: usize,
+    pub cmps: usize,
+    pub branches: usize,
+    pub rets: usize,
+}
+
+impl NoopBuilder {
+    pub fn new() -> Self { Self { consts: 0, binops: 0, cmps: 0, branches: 0, rets: 0 } }
+}
+
+impl IRBuilder for NoopBuilder {
+    fn begin_function(&mut self, _name: &str) {}
+    fn end_function(&mut self) {}
+    fn emit_param_i64(&mut self, _index: usize) { self.consts += 1; }
+    fn emit_const_i64(&mut self, _val: i64) { self.consts += 1; }
+    fn emit_const_f64(&mut self, _val: f64) { self.consts += 1; }
+    fn emit_binop(&mut self, _op: BinOpKind) { self.binops += 1; }
+    fn emit_compare(&mut self, _op: CmpKind) { self.cmps += 1; }
+    fn emit_jump(&mut self) { self.branches += 1; }
+    fn emit_branch(&mut self) { self.branches += 1; }
+    fn emit_return(&mut self) { self.rets += 1; }
+    fn emit_select_i64(&mut self) { self.binops += 1; }
+    fn emit_host_call_typed(&mut self, _symbol: &str, _params: &[ParamKind], has_ret: bool, _ret_is_f64: bool) { if has_ret { self.consts += 1; } }
+    fn emit_plugin_invoke(&mut self, _type_id: u32, _method_id: u32, _argc: usize, has_ret: bool) { if has_ret { self.consts += 1; } }
+    fn emit_plugin_invoke_by_name(&mut self, _method: &str, _argc: usize, has_ret: bool) { if has_ret { self.consts += 1; } }
+    fn ensure_local_i64(&mut self, _index: usize) { }
+    fn store_local_i64(&mut self, _index: usize) { self.consts += 1; }
+    fn load_local_i64(&mut self, _index: usize) { self.consts += 1; }
+}
+