fix: when headers() returns None in AsyncConfluentParser, replace it with an empty tuple

[andreaimprovised]

Description

Fixes #1459

Also, happens to fix a batch=False flow when headers() returns None now that I think about it.

Type of change

Please delete options that are not relevant.

• Documentation (typos, code examples, or any documentation updates)
• Bug fix (a non-breaking change that resolves an issue)
• New feature (a non-breaking change that adds functionality)
• Breaking change (a fix or feature that would disrupt existing functionality)
• This change requires a documentation update

Checklist

• My code adheres to the style guidelines of this project (scripts/lint.sh 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 scripts/test-cov.sh
  • I only ran the test that was added to cover this use case.
• I have ensured that static analysis tests are passing by running scripts/static-analysis.sh
  • I ensured that there were no new errors. This fixes two existing ones.
• I have included code examples to illustrate the modifications

Test

Just ran this test:

(venv) ➜  faststream git:(fix/1459) ✗ pytest -vv tests/brokers/confluent/test_consume.py -k test_consume_batch_headers
======================================================================================================== test session starts =========================================================================================================
platform darwin -- Python 3.12.3, pytest-8.2.0, pluggy-1.5.0 -- /Users/andreaimprovised/workspace/faststream/venv/bin/python
cachedir: .pytest_cache
rootdir: /Users/andreaimprovised/workspace/faststream
configfile: pyproject.toml
plugins: anyio-4.3.0, asyncio-0.23.6
asyncio: mode=Mode.STRICT
collected 16 items / 15 deselected / 1 selected

tests/brokers/confluent/test_consume.py::TestConsume::test_consume_batch_headers PASSED                                                                                                                                        [100%]

================================================================================================== 1 passed, 15 deselected in 3.62s ==================================================================================================

lint

(venv) ➜  faststream git:(fix/1459) ✗ scripts/lint.sh
Running ruff linter (isort, flake, pyupgrade, etc. replacement)...
All checks passed!
Running ruff formatter (black replacement)...
637 files left unchanged
Running codespell to find typos...
./docs/docs/en/release.md:42: aboout ==> about

static analysis

(venv) ➜  faststream git:(fix/1459) ✗ scripts/static-analysis.sh
Running mypy...
faststream/confluent/client.py:181: error: Argument 2 to "produce" of "Producer" has incompatible type "**Dict[str, Union[str, bytes, int, List[Tuple[str, Union[str, bytes]]]]]"; expected "Union[str, bytes, None]"  [arg-type]
faststream/confluent/client.py:181: error: Argument 2 to "produce" of "Producer" has incompatible type "**Dict[str, Union[str, bytes, int, List[Tuple[str, Union[str, bytes]]]]]"; expected "Optional[int]"  [arg-type]
faststream/confluent/client.py:181: error: Argument 2 to "produce" of "Producer" has incompatible type "**Dict[str, Union[str, bytes, int, List[Tuple[str, Union[str, bytes]]]]]"; expected "Optional[Callable[..., Any]]"  [arg-type]
faststream/confluent/client.py:181: error: Argument 2 to "produce" of "Producer" has incompatible type "**Dict[str, Union[str, bytes, int, List[Tuple[str, Union[str, bytes]]]]]"; expected "int"  [arg-type]
faststream/confluent/client.py:181: error: Argument 2 to "produce" of "Producer" has incompatible type "**Dict[str, Union[str, bytes, int, List[Tuple[str, Union[str, bytes]]]]]"; expected "Union[Dict[str, Union[str, bytes]], List[Tuple[str, Union[str, bytes]]], None]"  [arg-type]
faststream/confluent/client.py:396: error: Argument 1 to "run_async" has incompatible type "Callable[[int, Union[float, int]], List[TopicPartition]]"; expected "Union[Callable[[int, float], List[Optional[Message]]], Callable[[int, float], Awaitable[List[Optional[Message]]]]]"  [arg-type]
faststream/confluent/parser.py:31: error: Incompatible return value type (got "KafkaMessage", expected "StreamMessage[Message]")  [return-value]
faststream/confluent/parser.py:64: error: Incompatible return value type (got "KafkaMessage", expected "StreamMessage[Tuple[Message, ...]]")  [return-value]
faststream/confluent/subscriber/asyncapi.py:141: error: Overloaded function implementation does not accept all possible arguments of signature 1  [misc]
faststream/confluent/subscriber/asyncapi.py:141: error: Overloaded function implementation does not accept all possible arguments of signature 2  [misc]
faststream/confluent/publisher/asyncapi.py:128: error: Overloaded function implementation does not accept all possible arguments of signature 1  [misc]
faststream/confluent/publisher/asyncapi.py:128: error: Overloaded function implementation does not accept all possible arguments of signature 2  [misc]
faststream/confluent/broker/registrator.py:55: error: Incompatible types in assignment (expression has type "Dict[int, Union[AsyncAPIBatchSubscriber, AsyncAPIDefaultSubscriber]]", base class "ABCBroker" defined the type as "Mapping[int, SubscriberProto[Union[Message, Tuple[Message, ...]]]]")  [assignment]
faststream/confluent/broker/registrator.py:58: error: Incompatible types in assignment (expression has type "Dict[int, Union[AsyncAPIBatchPublisher, AsyncAPIDefaultPublisher]]", base class "ABCBroker" defined the type as "Mapping[int, PublisherProto[Union[Message, Tuple[Message, ...]]]]")  [assignment]
faststream/confluent/broker/registrator.py:1237: error: Argument 1 to "subscriber" of "ABCBroker" has incompatible type "Union[AsyncAPIDefaultSubscriber, AsyncAPIBatchSubscriber]"; expected "SubscriberProto[Union[Message, Tuple[Message, ...]]]"  [arg-type]
faststream/confluent/broker/registrator.py:1607: error: Argument 1 to "publisher" of "ABCBroker" has incompatible type "Union[AsyncAPIBatchPublisher, AsyncAPIDefaultPublisher]"; expected "PublisherProto[Union[Message, Tuple[Message, ...]]]"  [arg-type]
faststream/confluent/broker/registrator.py:1609: error: Argument 1 to "publisher" of "ABCBroker" has incompatible type "Union[AsyncAPIBatchPublisher, AsyncAPIDefaultPublisher]"; expected "PublisherProto[Union[Message, Tuple[Message, ...]]]"  [arg-type]
faststream/confluent/router.py:529: error: Argument "middlewares" to "__init__" of "BrokerRouter" has incompatible type "Iterable[Union[Callable[[Optional[Message]], BaseMiddleware], Callable[[Optional[Tuple[Message, ...]]], BaseMiddleware]]]"; expected "Iterable[Callable[[Union[Message, Tuple[Message, ...], None]], BaseMiddleware]]"  [arg-type]
faststream/confluent/broker/broker.py:60: error: Definition of "publisher" in base class "KafkaRegistrator" is incompatible with definition in base class "BrokerUsecase"  [misc]
faststream/confluent/fastapi/fastapi.py:374: error: Argument "middlewares" to "__init__" of "StreamRouter" has incompatible type "Iterable[Union[Callable[[Optional[Message]], BaseMiddleware], Callable[[Optional[Tuple[Message, ...]]], BaseMiddleware]]]"; expected "Iterable[Callable[[Union[Message, Tuple[Message, ...], None]], BaseMiddleware]]"  [arg-type]
faststream/confluent/testing.py:50: error: Argument 1 to "setup_subscriber" of "BrokerUsecase" has incompatible type "Union[AsyncAPIDefaultSubscriber, AsyncAPIBatchSubscriber]"; expected "SubscriberProto[Union[Message, Tuple[Message, ...]]]"  [arg-type]
Found 21 errors in 9 files (checked 240 source files)