Add changelog for release 0.40.0

Document notable changes for release 0.40.0, including new features, fixes, and breaking changes.

Author: Gsantomaggio

CHANGELOG.md

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+# Changelog
+
+All notable changes to this project will be documented in this file.
+
+## [[0.40.0](https://github.com/rabbitmq-community/rstream/releases/tag/v0.40.0)]
+
+This release focuses on improving stability during reconnection.
+
+## 0.40.0 - 2025-28-10
+- [Release 0.40.0](https://github.com/rabbitmq-community/rstream/releases/tag/v0.40.0) 
+
+### Added
+- Implement Auto recovery connection for consumer by @Gsantomaggio in [#250](https://github.com/rabbitmq-community/rstream/pull/250)
+- Implement producer recovery connection by @Gsantomaggio in [#251](https://github.com/rabbitmq-community/rstream/pull/251)
+- improve reconnection with metadata update handling by @Gsantomaggio in [#252](https://github.com/rabbitmq-community/rstream/pull/252)
+
+### Fixed
+- Fix subscribers list by @Gsantomaggio in [#246](https://github.com/rabbitmq-community/rstream/pull/246)
+- Restore flake8 test by @Gsantomaggio in [#244](https://github.com/rabbitmq-community/rstream/pull/244)
+
+### Changed
+- Refactor the producers list replace the reference with the id as map key by @Gsantomaggio in [#249](https://github.com/rabbitmq-community/rstream/pull/249)
+- Update dependencies by @Gsantomaggio in [#243](https://github.com/rabbitmq-community/rstream/pull/243)
+
+### Removed
+- Remove `reconnect_stream`
+- Removed `message_context.consumer.get_stream(message_context.subscriber_name)` in favour of `message_context.stream`
+
+### Breaking changes
+- The `reconnect_stream` function has been removed. Use the auto-recovery feature instead.
+- The `message_context.consumer.get_stream(message_context.subscriber_name)` method has been removed.
+- Use `message_context.stream` to access the stream directly.
+- The subscribe function now returns the `subscription_id` that you can use to unsubscribe.