This change introduces two new interceptors with callback methods
for concurrent request handling. These interfaces are
CallableProcessingInterceptor and DeferredResultProcessingInterceptor.
Unlike a HandlerInterceptor, and its AsyncHandlerInterceptor sub-type,
which intercepts the invocation of a handler in he main request
processing thread, the two new interfaces are aimed at intercepting the
asynchronous execution of a Callable or a DeferredResult.
This allows for the registration of thread initialization logic in the
case of Callable executed with an AsyncTaskExecutor, or for centralized
tracking of the completion and/or expiration of a DeferredResult.
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