sds: Implement logic for tracking sent messages

[adklempner]

Implement logic for sending and delivering messages.

Key implementation tasks:

1. Create message preparation function that:

   • Increments and assigns Lamport timestamp for the channel
   • Extracts recent message IDs from local log for causal history
   • Gets current serialized Bloom filter state
   • Generates unique message ID
   • Assembles complete Message object

2. Implement outgoing message handling:

   • Add message to unacknowledged outgoing buffer for channel
   • Track message state for acknowledgment/retry
   • Handle buffer size limits and cleanup
   • Maintain message ordering guarantees

3. Add broadcast mechanism that:

   • Supports multiple transport methods
   • Handles serialization of Message object
   • Provides proper error handling
   • Includes retry logic for failed sends
   • Supports test environment simulation

4. Implement message delivery logic:

   • Update local Lamport timestamp based on received message timestamp
   • Sort messages by Lamport timestamp
   • Break timestamp ties using messageID comparison
   • Insert messages into local log maintaining order
   • Trigger delivery callbacks/events
   • Handle delivery of buffered messages when dependencies are met

5. Create test infrastructure:

   • Mock transport layer
   • Verify message preparation correctness
   • Test causal history extraction
   • Validate Lamport timestamp behavior
   • Confirm proper buffer management
   • Test message ordering and delivery sequences
   • Verify tie-breaking behavior

The implementation should maintain causal ordering guarantees while being resilient to network issues and message delivery failures.