structlog 26.1.0: Prove that `structlog` binding APIs do not mutate an existing logger instance.

# Notes

`search_known_solution` returned a compatible existing sample for structlog integration (`case:sha256:2d6ee21327f92d4ac51657e55ce179714708af915d368fe18433a80d9aa7931b`), which proves `dictConfig`, `ProcessorFormatter` placement, and `disable_existing_loggers` interaction.

A naive model would expect `logger.bind(...)` to mutate the same logger instance, which in this sample fails with `assert logger is not logger_bound`.

{"case":{"believed":"A caller expects `bind` to mutate the original logger and return that same object.","caseId":"case:sha256:3ca7fa9e3d5ded6c84380644920e11eef657e22a113ebdd6fc93437c424169a2","contract":["assert logger is not logger_bound","assert captured[0].get('user') == 'alice'","assert 'user' not in captured[1]"],"goal":"Prove that `structlog` binding APIs do not mutate an existing logger instance.","kind":"HOW","packages":["pkg:pypi/structlog@26.1.0"],"schemaVersion":1,"symbols":["structlog.get_logger","structlog.configure","structlog.testing.capture_logs"]},"contractCommand":["python","test/contract.py"],"environment":{"arch":"x64","ecosystem":"pypi","executionContext":"python","language":"python","os":"linux","packageManager":"pip","runtime":"python","schemaVersion":1},"license":"MIT-0","packages":["pkg:pypi/structlog@26.1.0"],"schemaVersion":1,"symbols":["structlog.get_logger","structlog.configure","structlog.testing.capture_logs"],"verifierAdapter":"python@1"}

structlog==26.1.0

import structlog
from structlog.testing import CapturingLoggerFactory, capture_logs


def main() -> None:
    structlog.configure(processors=[], logger_factory=CapturingLoggerFactory())

    logger = structlog.get_logger()
    logger_bound = logger.bind(user="alice")

    with capture_logs() as captured:
        logger_bound.info("bound event")
        logger.info("plain event")

    assert logger is not logger_bound
    assert captured[0].get("user") == "alice"
    assert "user" not in captured[1]


if __name__ == "__main__":
    main()