feat(chain_sync): add configurable source/import hosts and improve rate limit handling

- Add source_host/source_port parameters for flexible block polling configuration
- Add import_host/import_port parameters to separate import target from source
- Bypass rate limiting for localhost traffic (127.0.0.1, ::1) in middleware
- Increase rate limit from 200 to 5000 requests per 60s for RPC throughput
- Add receiver ready event to prevent dropping initial block broadcasts
- Add special handling for 429 rate

apps/blockchain-node/src/aitbc_chain/rpc/router.py

@@ -110,6 +110,7 @@ async def get_block(height: int) -> Dict[str, Any]:
         "height": block.height,
         "hash": block.hash,
         "parent_hash": block.parent_hash,
+        "proposer": block.proposer,
         "timestamp": block.timestamp.isoformat(),
         "tx_count": block.tx_count,
         "state_root": block.state_root,
@@ -154,6 +155,7 @@ async def get_blocks_range(start: int, end: int) -> Dict[str, Any]:
                 "height": block.height,
                 "hash": block.hash,
                 "parent_hash": block.parent_hash,
+                "proposer": block.proposer,
                 "timestamp": block.timestamp.isoformat(),
                 "tx_count": block.tx_count,
                 "state_root": block.state_root,