feat: Improve Mycelium slave and streamer communication

- Renamed the topic for database synchronization messages from
  'db_sync' to 'sync_db' for clarity.
- Updated the Mycelium slave to decode base64 payload before
  processing and to log received messages and their source.
- Added logging to the Mycelium streamer to track sent messages.
- Added a new feature to retrieve and log the last index from the
  worker after syncing updates.  This improves monitoring and
  debugging capabilities.

examples/data/deduped_mycelium_slave.vsh

@@ -9,6 +9,8 @@ import os
 import encoding.base64
 import json
 
+// TODO: Make the worker read the data from the streamer instead.
+
 const slave_port = 9000
 const master_public_key = '89c2eeb24bcdfaaac78c0023a166d88f760c097c1a57748770e432ba10757179'
 const master_address = '458:90d4:a3ef:b285:6d32:a22d:9e73:697f'
@@ -39,9 +41,16 @@ defer {
 
 // Receive messages
 // Parameters: wait_for_message, peek_only, topic_filter
-received := slave.receive_msg(wait: true, peek: false, topic: 'db_sync')!
+received := slave.receive_msg(wait: true, peek: false, topic: 'sync_db')!
 println('Received message from: ${received.src_pk}')
 println('Message payload: ${base64.decode_str(received.payload)}')
 
-payload := received.payload
-worker.sync_updates(payload.bytes()) or { error('Failed to sync updates to worker due to: ${err}') }
+payload := base64.decode(received.payload)
+println('Payload: ${payload.str()}')
+worker.sync_updates(received.payload.bytes()) or {
+	error('Failed to sync updates to worker due to: ${err}')
+}
+
+// Get last index
+last_index := worker.get_last_index()!
+println('Last index: ${last_index}')