Enhance handling of large eventlogs

**Original reporter**: _jan.stolarek@_

When I enable detailed spark logging via -lf flag I end up with huge eventlog files (130MB). Attempting to load these into ThreadScope practically kills my OS - memory runs out, swapping begins and I am forced to kill TS (which takes some time before the OS actually responds and kills the process). This makes -lf flag useless for my program and I think this might not be uncommon situation. It would be good if TS supported some sort of lazy loading of big eventlogs, so users could at least view parts of the log.

该 issue 涉及加载使用 -lf flag 生成的大型 eventlog 文件，但没有指出相关的文件、测试或加载入口。首先跟踪 ThreadScope 如何打开并保留 eventlog，然后确定用户应如何查看日志的一部分而不耗尽内存。当一个 130MB 的 eventlog 能够被打开和检查且不再出现当前的内存故障时，即视为完成。

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