Add Atomic Publish Support

[mtmk]

This pull request adds support for the new AllowAtomicPublish property in the JetStream stream configuration as described in ADR-50, allowing atomic batch publishing into streams. It also includes comprehensive tests to verify the correct behavior of this property when creating, updating, and retrieving streams.

JetStream Stream Configuration Enhancements:

• Added the AllowAtomicPublish property to the StreamConfig class, enabling atomic batch publishing for streams. This property is serialized to JSON as allow_atomic and is ignored when set to its default value.

Testing Improvements:

• Introduced a new test, AllowAtomicPublish_property_should_be_set_on_stream, in ManageStreamTest.cs to verify that the AllowAtomicPublish property is correctly set, updated, and persisted on streams. The test is conditionally skipped for NATS server versions earlier than 2.12.
• Added a missing using directive for NATS.Client.TestUtilities in the test file to support the new test.

[Copilot]

Pull Request Overview

This pull request implements the new AllowAtomicPublish property for NATS JetStream streams as specified in ADR-50, enabling atomic batch publishing functionality. The changes add the necessary property to the StreamConfig model and include comprehensive testing to verify the feature works correctly.

Key changes:

• Added the AllowAtomicPublish boolean property to StreamConfig with proper JSON serialization
• Implemented comprehensive tests covering stream creation, retrieval, and updates with the new property
• Added conditional test skipping for NATS server versions prior to 2.12 where this feature is not available

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/NATS.Client.JetStream/Models/StreamConfig.cs	Added AllowAtomicPublish property with JSON serialization attributes
tests/NATS.Client.JetStream.Tests/ManageStreamTest.cs	Added comprehensive test coverage and missing using directive

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}

[scottf]

LGTM