[fix][client] Producer uses pulsar-client-internal thread to execute callback

[nodece]

Fixes #21900

Motivation

In #21900, I guess the user uses a sync call in the pulsar-client-io callback thread, so throw the timeout exception.

The pulsar-client-io thread is used to communicate between the broker and the client, when pulsar-client-io is stuck, the timeout exception will be thrown.

If we switch from the pulsar-client-io to the pulsar-client-internal thread to execute the callback, #21900 will be fixed.

In the consumer, there's a similar approach： https://github.com/apache/pulsar/blob/252509e08018eeed189e0d5492c3664a67bced06/pulsar-client/src/main/java/org/apache/pulsar/client/impl/ConsumerImpl.java#L471-L487

Another approach: Please use the same call(sync or async) in your project.

Modifications

• Producers always use the pulsar-client-internal thread to execute the callback.

Verifying this change

ProducerCallbackThreadTest has been added.

Documentation

• [ ] doc
• [ ] doc-required
• [x] doc-not-needed
• [ ] doc-complete

[nodece]

Some tests fail when multiple threads are used to execute callbacks.

[nodece]

/pulsarbot rerun-failure-checks