* The `EncoderInterface` and `DecoderInterface` have been replaced by a unified `Symfony\Component\Messenger\Transport\Serialization\SerializerInterface`.
* The locator passed to `ContainerHandlerLocator` should not prefix its keys by "handler." anymore
* The `AbstractHandlerLocator::getHandler()` method uses `?callable` as return type
* Renamed `EnvelopeItemInterface` to `StampInterface`
*`Envelope`'s constructor and `with()` method now accept `StampInterface` objects as variadic parameters
* Renamed and moved `ReceivedMessage`, `ValidationConfiguration` and `SerializerConfiguration` in the `Stamp` namespace