Introduce Neo.core.Base#observeConfig() for Lifecycle-Aware Config Subscriptions

Problem: Manually managing Neo.core.Config subscriptions within Neo.core.Base instances is error-prone. Developers must remember to explicitly unsubscribe, leading to potential memory leaks if cleanup is missed.

Solution: Add a new public method observeConfig(publisher, configName, fn) to Neo.core.Base. This method will:

1. Accept a publisher (instance or ID), a configName (string), and a callback fn.
2. Internally resolve the publisher to an instance.
3. Retrieve the Neo.core.Config controller for the specified configName on the publisher.
4. Call Neo.core.Config#subscribe using this.id (the subscribing Base instance's ID) as the subscription id.
5. Store the returned cleanup function in a new private array (#configSubscriptionCleanups) on this (the subscribing Base instance).
6. Integrate the cleanup of #configSubscriptionCleanups into Neo.core.Base#destroy(), ensuring automatic unsubscription.

Benefits:

• Automatic Memory Leak Prevention: Subscriptions are automatically cleaned up when the subscribing Base instance is destroyed, eliminating a common source of leaks.
• Simplified Developer Experience: Provides a single, intuitive, and consistent API for subscribing to configs on other instances.
• Centralized Management: Consolidates subscription logic within Base, reducing boilerplate and potential errors in subclasses.
• Discourages Self-Observation: Includes a JSDoc warning example, guiding developers towards using afterSet<ConfigName>() hooks for internal reactions.

Impact: Replaces direct calls to Neo.core.Config#subscribe in Neo.core.Base subclasses with the new observeConfig method.