chore: make deprecated field optional

Author: janniks

src/event-stream/core-node-message.ts

@@ -242,7 +242,7 @@ export interface CoreNodeTxMessage {
   tx_index: number;
   contract_interface: ClarityAbi | null;
   /** @deprecated Use `contract_interface` instead. The node renamed `contract_abi` to `contract_interface`. */
-  contract_abi: ClarityAbi | null;
+  contract_abi: ClarityAbi | null | undefined;
   execution_cost: CoreNodeExecutionCostMessage;
   microblock_sequence: number | null;
   microblock_hash: string | null;