fix a ClassCastException when scheduling to look up

[Yimiun]

Motivation

new ExecutorProvider(proxyConfig.getLookupThreadPoolNum(), "mop-lookup-thread") ; It will create a FinalizableDelegatedExecutorService

(ScheduledExecutorService) executorProvider.getExecutor();

It can't be cast to a ScheduledExecutorService, and it will create a RuntimeException without catch, which is also blocking the proxy thread

Documentation

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[github-actions[bot]]

@Yimiun:Thanks for your contribution. For this PR, do we need to update docs? (The PR template contains info about doc, which helps others know more about the changes. Can you provide doc-related info in this and future PR descriptions? Thanks)

[Technoboy-]

Thanks @Yimiun