Fix: Clarify the behavior of concurrent requests in QueuedInterceptor (…

…#2347)

The previous documentation for `QueuedInterceptor` could lead to misunderstandings about how concurrent requests are handled. The explanation suggested that requests would have to wait for the previous request to complete before being initiated.

This update clarifies that requests are processed in three independent queues: `onRequest`, `onResponse`, and `onError`. These queues run in parallel.

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Signed-off-by: 友人A <58846244+Passer-by@users.noreply.github.com>
Co-authored-by: Alex Li <github@alexv525.com>

dio/lib/src/interceptor.dart

@@ -374,7 +374,9 @@ class _TaskQueue<T, V extends _BaseHandler> {
 
 /// [Interceptor] in queue.
 ///
-/// Concurrent requests will be added to the queue for interceptors.
+/// `onRequest`, `onResponse`, and `onError` are processed in separate queues
+/// when running concurrent requests. These queues run in parallel,
+/// new requests can be initiated before previous have been completed.
 class QueuedInterceptor extends Interceptor {
   final _requestQueue = _TaskQueue<RequestOptions, RequestInterceptorHandler>();
   final _responseQueue = _TaskQueue<Response, ResponseInterceptorHandler>();
@@ -430,7 +432,7 @@ class QueuedInterceptor extends Interceptor {
   }
 }
 
-/// A helper class to create queued-interceptors in ease.
+/// A helper class to create [QueuedInterceptor] in ease.
 ///
 /// See also:
 ///  - [InterceptorsWrapper], creates [Interceptor]s in ease.