feat: add on_assign, on_revoke, on_lost callbacks for Confluent subscriber

[Br1an67]

Description

Add rebalance callback parameters (on_assign, on_revoke, on_lost) to the Confluent subscriber, allowing users to monitor partition assignment/revocation events without monkey-patching AsyncConfluentConsumer.

These callbacks are passed directly to confluent_kafka.Consumer.subscribe().

Usage:

@broker.subscriber(
    "my-topic",
    on_assign=lambda consumer, partitions: print(f"Assigned: {partitions}"),
    on_revoke=lambda consumer, partitions: print(f"Revoked: {partitions}"),
    on_lost=lambda consumer, partitions: print(f"Lost: {partitions}"),
)
async def handler(body: str):
    print(body)

Fixes #1676

Type of change

• New feature (a non-breaking change that adds functionality)

Checklist

• My code adheres to the style guidelines of this project (just lint shows no errors)
• I have conducted a self-review of my own code
• I have made the necessary changes to the documentation
• My changes do not generate any new warnings
• I have added tests to validate the effectiveness of my fix or the functionality of my new feature
• Both new and existing unit tests pass successfully on my local environment by running just test-coverage
• I have ensured that static analysis tests are passing by running just static-analysis
• I have included code examples to illustrate the modifications