[FFI][Reflection] Lazily resolve KWARGS sentinel in auto-init (#519)

This PR intends to avoid the eager lookup of `ffi.GetKwargsObject`
during `MakeInit` construction. Instead, it resolves and caches the
KWARGS sentinel via a function-local static (`GetKwargsSentinel`) when
`__ffi_init__` is invoked. This removes static-init order dependence
between reflection auto-init registration and global function
registration, preventing `Function ffi.GetKwargsObject not found`
failures.

Author: akaashrp

include/tvm/ffi/reflection/init.h

@@ -62,6 +62,15 @@ TObjectRef FFIConvertFromAnyViewToObjectRef(AnyView input) {
                            << "` to `" << TypeTraits<TObjectRef>::TypeStr() << "`";
 }
 
+/*!
+ * \brief Return the lazily initialized KWARGS sentinel object.
+ */
+inline const ObjectRef& GetKwargsSentinel() {
+  static ObjectRef kwargs_sentinel =
+      Function::GetGlobalRequired("ffi.GetKwargsObject")().cast<ObjectRef>();
+  return kwargs_sentinel;
+}
+
 }  // namespace details
 
 /*!
@@ -118,12 +127,9 @@ inline Function MakeInit(int32_t type_index) {
   std::stable_partition(info->pos_indices.begin(), info->pos_indices.end(),
                         [&](size_t idx) { return !info->all_fields[idx].has_default; });
 
-  // Eagerly resolve the KWARGS sentinel via global function registry.
-  ObjectRef kwargs_sentinel =
-      Function::GetGlobalRequired("ffi.GetKwargsObject")().cast<ObjectRef>();
-
   return Function::FromPacked(
-      [info, kwargs_sentinel, type_info](PackedArgs args, Any* rv) {
+      [info, type_info](PackedArgs args, Any* rv) {
+        const ObjectRef& kwargs_sentinel = details::GetKwargsSentinel();
         // ---- 1. Create object via CreateEmptyObject --------------------------
         ObjectPtr<Object> obj_ptr = CreateEmptyObject(type_info);