Add processors param to capture_logs()

[l1nd3r0th]

Summary

Dear Hynek,

Thanks for building and maintaining structlog!

I'm using a pytest fixture to capture logs in an application test suite. In some test cases it's convenient to be able to inspect context variables.

This PR, if accepted, enables capture_logs() to capture logs with context variables like this:

@pytest.fixture(name="log_output")
def fixture_log_output() -> Iterator[LogMatcher]:
    with capture_logs(
        processors=[
            structlog.contextvars.merge_contextvars,
        ]
    ) as logs:
        yield LogMatcher(captured_logs=logs)

Or whatever other interesting processing people might like to do. :)

I realize I probably could have gotten the same result by configuring processors in a fixture, as shown in the docs, something like:

@pytest.fixture(name="log_output")
def fixture_log_output():
    return LogCapture()

@pytest.fixture(autouse=True)
def fixture_configure_structlog(log_output):
    structlog.configure(
        processors=[structlog.contextvars.merge_contextvars, log_output]
    )

...but I like how capture_logs() restores the configuration after itself.

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[hynek]

Cool, thanks – I've completely forgotten about capture_logs. :)

Sorry for the long delay, it's been busy. :|