sds: Implement periodic maintenance tasks for incoming and outgoing buffers

[adklempner]

1. Create dependency resolution system:

   • Scan incoming buffer for messages with missing dependencies
   • Track age of pending messages
   • Request missing messages from peers
   • Prioritize older pending messages
   • Handle timeout/failure cases for unresolvable dependencies

2. Implement unacknowledged message management:

   • Track age of unacknowledged outgoing messages
   • Implement priority-based rebroadcast strategy
   • Handle messages that exceed retry limits
   • Manage buffer size through pruning old messages
   • Track successful redelivery attempts