GHSA-cc7c-9jff-58wj: djust: Client mass-assignment of arbitrary view attributes via the default dj-model update_model handler

### Impact `djust.mixins.model_binding.ModelBindingMixin` provides a default `update_model` event handler and is part of the **LiveView base MRO**, so every LiveView exposes it. It `setattr`s a view attribute whose **name is client-supplied** (`field`), gated only by: reject `_`-prefixed names; reject a **14-entry denylist** of framework internals (`FORBIDDEN_MODEL_FIELDS`); optional `allowed_model_fields` which **defaults to None = allow all**; and `hasattr` existence. …