[jsonbailey]

feat: Remove the experimental AsyncHook class

Warning

Breaking change to the experimental async API. Code that subclasses AsyncHook or passes AsyncHook instances to AsyncLDClient must change to use ldclient.hook.Hook. The async API is experimental, so this is not marked with ! and does not need a major version. Edit the release notes to call out the break for async users.

Summary

AsyncLDClient now uses the same ldclient.hook.Hook as LDClient, so existing integrations such as the OpenTelemetry tracing hook work with the async client. Before this change, the async client accepted only AsyncHook and ignored sync hooks.

• The async client runs the hook stages synchronously in the caller's task. A span or context variable set in the before stage stays current until the after stage.
• AsyncHook is removed. The async API is experimental.
• If an evaluation is cancelled or raises, the after stages still run, with an error detail and the default value. The exception is then re-raised. A tracing hook can then end its span.
• AsyncPlugin keeps its async register(). Its get_hooks() now returns Hook instances.
• AsyncConfig and add_hook() ignore items of the wrong type, the same as the sync client.
• The async contract-test service uses the sync PostingHook.