consensus: improve block proposal timing and return status, fix transaction field mapping in sync

- Add initial sleep before first proposal to prevent immediate block creation
- Return bool from _propose_block to indicate if block was actually proposed
- Wait for next slot only after successful proposal, use regular interval after skipped proposals
- Add 1s sleep after proposal errors to prevent tight error loops
- Add parent_hash, proposer, and state_root fields to /rpc/blocks-range response
- Fix transaction field mapping

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

@@ -288,10 +288,9 @@ class ChainSync:
         # Import transactions if provided and apply state changes
         if transactions:
             for tx_data in transactions:
-                sender_addr = tx_data.get("sender", "")
-                payload = tx_data.get("payload", {}) or {}
-                recipient_addr = payload.get("to") or tx_data.get("recipient", "")
-                value = int(payload.get("value", 0) or 0)
+                sender_addr = tx_data.get("from", "")
+                recipient_addr = tx_data.get("to", "")
+                value = int(tx_data.get("amount", 0) or 0)
                 fee = int(tx_data.get("fee", 0) or 0)
                 tx_hash = tx_data.get("tx_hash", "")