Add name attribute to BytesLogger

[veeceey]

Summary

• Fixes AttributeError: 'BytesLogger' object has no attribute 'name' when using add_logger_name processor with BytesLoggerFactory (closes AttributeError: 'BytesLogger' object has no attribute 'name' #734)
• Adds a name slot to BytesLogger and accepts it as a keyword-only argument in __init__
• Updates BytesLoggerFactory.__call__ to forward the first positional argument (the logger name from get_logger()) to BytesLogger

Details

As reported in #734, using structlog.stdlib.add_logger_name with BytesLoggerFactory crashes because BytesLogger has no name attribute. The add_logger_name processor accesses logger.name when no _record is present in the event dict.

This implements the fix suggested by @hynek in #734 (comment) with one additional safety guard: BytesLoggerFactory.__call__ uses args[0] if args else None to avoid an IndexError when no positional arguments are passed to the factory.

Test plan

• Added TestBytesLogger::test_name_attribute -- verifies BytesLogger accepts a name kwarg
• Added TestBytesLogger::test_name_defaults_to_none -- verifies default is None
• Added TestBytesLoggerFactory::test_passes_name_from_args -- verifies factory forwards name
• Added TestBytesLoggerFactory::test_name_defaults_to_none -- verifies no-arg case
• Added TestBytesLoggerFactory::test_extra_args_ignored -- verifies extra args beyond first are ignored
• Added TestAddLoggerName::test_logger_name_added_with_bytes_logger -- end-to-end test with named BytesLogger
• Added TestAddLoggerName::test_logger_name_none_with_unnamed_bytes_logger -- end-to-end test with unnamed BytesLogger
• All existing tests pass (125 in test_output.py, 139 in test_stdlib.py)

[veeceey]

Hi @hynek, friendly ping on this PR. It's been open for about 10 days now without any review activity. Would appreciate any feedback when you have a moment -- happy to adjust if anything needs changing. Thank you!