feat: support blocking send_non_blocking() and other RPCs

[BewareMyPower]

Fixes #342

Motivation

#312 changes connection's outbound channel from unbounded to bounded and once the channel is full, all RPC requests will fail with the SlowDown error. However, other RPCs like Ack could also be affected. This is different from other Pulsar client SDKs because only pending Send RPCs should be limited.

This behavior is not documented and hence very confusing.

Modifications

Add a block_if_queue_full option to simulate the feature from Java client:
https://github.com/apache/pulsar/blob/14543d3fde935d1b70e3707a8b2c0294eb53dccb/pulsar-client-api/src/main/java/org/apache/pulsar/client/api/ProducerBuilder.java#L241

• For Send RPC
  • call async_channel::Sender::send when this option is enabled (disabled by default)
  • keep calling async_channel::Sender::try_send and fail with SlowDown if queue is full
• For other RPCs: call async_channel::Sender::send

Add block_if_queue_full to show the difference between the option is enabled and disabled.

Additionally, add documents to this new option, as well as send_non_blocking because it's hard for users to know how to handle this SlowDown error without the documentation.

[Copilot]

Pull Request Overview

This PR adds support for blocking behavior when the internal pending queue is full during send operations, addressing issue #342. The change allows users to choose between blocking and non-blocking behavior when the outbound channel reaches capacity.

• Adds block_queue_if_full option to ProducerOptions to control blocking behavior for send operations
• Modifies connection logic to differentiate between send RPCs (which can fail fast) and other RPCs (which should block)
• Enhances documentation for the new option and existing send_non_blocking method with usage examples

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/producer.rs	Adds block_queue_if_full option, updates documentation with usage examples, and includes comprehensive tests
src/connection.rs	Refactors message sending logic to support both blocking and non-blocking modes based on the new parameter
src/client.rs	Adds documentation for the with_outbound_channel_size method

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[Copilot]

Pull Request Overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

Comments suppressed due to low confidence (1)

src/producer.rs:149

• Typo in comment: 'treshold' should be 'threshold'.

    /// batch size in bytes treshold (only relevant when batch_size active).

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[FlorentinDUBOIS]

Thank that a great addition!