合约事件推送的SampleCode中BlockNumber是BigInteger所以直接复制过来用会编译错误

https://fisco-bcos-doc.readthedocs.io/zh-cn/latest/docs/sdk/java_sdk/event_sub.html#id7

几个示例中的Block参数是BigInteger，所以编译的时候报错。
```java
// 全部Event fromBlock设置为 -1
params.setFromBlock(-1); //应该是==> params.setFromBlock(new BigInteger("-1"));

// toBlock设置为-1，处理至最新区块继续等待新的区块
params.setToBlock(-1); //应该是==> params.setToBlock(new BigInteger("-1"));
```

Open the linked event-subscription documentation and inspect the sample code containing the fromBlock and toBlock assignments. Update the examples so their -1 values match the BigInteger parameter type, then verify that the copied Java snippets no longer produce the reported compilation error.

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