feat(chain_sync): add retry logic with exponential backoff for RPC connections and block imports

- Add retry mechanism with exponential backoff for block broadcast loop
- Implement max 5 retries with 2s base delay for RPC connection failures
- Reset retry count on successful connection
- Add 20s wait period after max retries before resetting counter
- Add retry logic for block import with 3 attempts and 1s base delay
- Handle non-200 HTTP responses as exceptions to trigger retries
- Improve error logging

apps/blockchain-node/src/aitbc_chain/main.py

@@ -148,7 +148,11 @@ class BlockchainNode:
             max_size=settings.mempool_max_size,
             min_fee=settings.min_fee,
         )
-        self._start_proposers()
+        # Start proposers only if enabled (followers set enable_block_production=False)
+        if getattr(settings, "enable_block_production", True):
+            self._start_proposers()
+        else:
+            logger.info("Block production disabled on this node", extra={"proposer_id": settings.proposer_id})
         await self._setup_gossip_subscribers()
         try:
             await self._stop_event.wait()