docs: add migration guide for v4 to v5

docs/book/v5/migration/v4-to-v5.md

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+# Migration from Version 4 to 5
+
+## Changed Behavior & Signature Changes
+
+### Final Classes and Inheritance
+
+As a best practice, even if a hydrator (or other classes) is not marked as `final` in this library, extending it is discouraged — future major releases may prohibit inheritance altogether.
+Prefer **composition over inheritance** by combining small, focused objects.
+Use **decorators** to extend behavior without modifying original classes or creating deep inheritance chains.
+
+### Hydrator Plugin Manager
+
+#### Removal of legacy Zend aliases
+
+All aliases that referenced the equivalent, legacy "Zend" hydrators have been removed. This means that an exception will be thrown if you attempt to retrieve a hydrator using one of these aliases such as `Zend\Hydrator\ArraySerializableHydrator::class`.
+
+You will need to either update your codebase to use known aliases such as `Laminas\Hydrator\ArraySerializableHydrator::class`, or re-implement the aliases in your configuration.
+
+### Removed Exceptions
+
+The following exceptions have been removed:
+
+- `Laminas\Hydrator\Exception\ExtensionNotLoadedException`
+- `Laminas\Hydrator\Exception\InvalidCallbackException`
+- `Laminas\Hydrator\Exception\LogicException`
+
+### Changes of `Laminas\Hydrator\Strategy\SerializableStrategy`
+
+- Simplified implementation.
+- Internal getter and setter methods have been removed.
+- If you're relying on these, update your code to use serialization logic externally or via injected services.
+
+### Changes to Individual Hydrators
+
+The following deprecated classes (since version 3.0.0) have been removed in version 5.  
+Please update your codebase to use the corresponding `*Hydrator` classes:
+
+| Removed Class                              | Replacement Class                                  |
+|-------------------------------------------|----------------------------------------------------|
+| `Laminas\Hydrator\ArraySerializable`      | `Laminas\Hydrator\ArraySerializableHydrator`       |
+| `Laminas\Hydrator\ClassMethods`           | `Laminas\Hydrator\ClassMethodsHydrator`            |
+| `Laminas\Hydrator\ObjectProperty`         | `Laminas\Hydrator\ObjectPropertyHydrator`          |
+| `Laminas\Hydrator\Reflection`             | `Laminas\Hydrator\ReflectionHydrator`              |