Use a descriptive .expect("...") instead of bare .unwrap() in test: src/config.rs:1905

[Markadrian6399]

// src/config.rs:1905
assert_eq!(ListenerMode::parse("STREAM").unwrap(), ListenerMode::Stream);

This is test code, so panicking on failure is expected behavior -- not a
production risk. But a bare .unwrap() gives no context when the test
fails (just "called Result::unwrap() on an Err value" with no
indication of what was being asserted). Replacing it with
.expect("...") and a short message describing the expected condition
makes test failures faster to diagnose from CI logs alone.