relaystr/ndk

AI Summary: Implement a flexible mechanism within the Dart Nostr Development Kit (NDK) allowing users to inject custom code to process notes after network retrieval but before caching. This involves creating 'transformers' – user-defined functions that can modify or filter notes based on specific criteria. These transformers should be applicable to both `PostNoteProcessor` and `PostNetworkProcessor` contexts.

AI Summary: Implement a streaming solution for retrieving follower information in the Dart Nostr Development Kit (NDK). The current method of looking up followers can be slow, so the goal is to create a mechanism that streams follower data to the UI, improving performance and user experience.