Improve asynchronous producer with more options for creation and send

[BewareMyPower]

Fixes#261

[BewareMyPower]

This PR is based on #277, so wait for #277 to be merged first

[Copilot]

Pull request overview

This PR enhances the asyncio producer API with additional configuration options and message sending capabilities to align with the synchronous producer API. It adds support for message properties, routing keys, delayed delivery, flush operations, and exposes producer metadata methods.

Key changes:

• Extended Producer.send() with parameters for properties, partition/ordering keys, sequence IDs, replication settings, and delayed delivery
• Added Producer.flush() method for asynchronous batch flushing
• Exposed producer metadata via topic(), producer_name(), and last_sequence_id() methods
• Enhanced Client.create_producer() with comprehensive configuration options including batching, compression, encryption, access modes, and message routing

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
tests/asyncio_test.py	Added tests for producer name/topic retrieval, keyed message sending with properties, and flush functionality with batching validation
src/producer.cc	Added Python binding for flush_async method to enable asynchronous flush operations
pulsar/asyncio.py	Extended Producer class with send options, flush method, and metadata accessors; enhanced Client.create_producer() with comprehensive configuration parameters matching the synchronous API

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