feat(performance): Make non-strict mode faster for classes. Addresses #1071

Immer 10.x solved slow iteration for plain JS objects. This update applies the same handling to class instances. In cases this makes class instance handling 3 times faster. Note that this slightly modifies the behavior of Immer with classes in obscure corner cases, in ways that match current documentation, but do not match previous behavior. If you run into issues with this release icmw. class instances, use `setUseStrictShallowCopy("class_only")` to revert to the old behavior. For more details see https://immerjs.github.io/immer/complex-objects#semantics-in-detail