优化 CtSph#lookProcessChain 创建拦截链方法（减少第一次创建拦截链时持有锁的占用时间，提升 rt，减少 gc 压力）

Original logic:

chainMap is a Map with the volatile modifier. When the first time to get the ProcessorSlotChain, if it is empty, the old logic enters the synchronization block, creates a new map, and then copies the original data by putAll, finally completely replaces the chainMap, achieving visibility through volatile replacement of references.