config: add option to prevent empty block proposals and improve genesis block handling

- Add propose_only_if_mempool_not_empty config option (default: True) to skip block proposals when mempool is empty
- Add detailed logging for transaction processing in block proposals (sender/recipient validation, balance checks, duplicate detection)
- Check for existing transactions in database before adding to prevent duplicates
- Improve genesis block creation: check by height and hash, use "genesis" as proposer to avoid hash conflicts
- Add proper error handling and rollback for

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

@@ -43,6 +43,9 @@ class ChainSettings(BaseSettings):
     max_block_size_bytes: int = 1_000_000  # 1 MB
     max_txs_per_block: int = 500
 
+    # Only propose blocks if mempool is not empty (prevents empty blocks)
+    propose_only_if_mempool_not_empty: bool = True
+
     # Monitoring interval (in seconds)
     blockchain_monitoring_interval_seconds: int = 60
     min_fee: int = 0  # Minimum fee to accept into mempool