Replace time crate with jiff

[Copilot]

Removes the time crate dependency by switching from simplelog to fern for logging, with jiff providing timestamp formatting.

Changes

• Dependencies: Replaced simplelog with fern 0.7.1 and jiff 0.2.18
• Logging: Custom fern::Dispatch formatter using jiff::Zoned::now() for timestamps

fern::Dispatch::new()
    .level(log::LevelFilter::Debug)
    .format(|formatter_out, log_msg, log_rec| {
        let when = jiff::Zoned::now();
        formatter_out.finish(format_args!(
            "[{} {} {}:{}] {}",
            when.strftime("%Y-%m-%d %H:%M:%S%.3f %:z"),
            log_rec.level(),
            log_rec.file().unwrap_or("<unknown>"),
            log_rec.line().unwrap_or(0),
            log_msg
        ))
    })
    .chain(log_output)
    .apply()?;

Log format remains functionally equivalent with timezone-aware timestamps.

Original prompt

Switch the time crate with jiff.

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[Byron]

Old

04:41:37 [INFO] dua options=Args {
    command: None,
    threads: 3,
    format: Metric,
    apparent_size: false,
    count_hard_links: false,
    stay_on_filesystem: false,
    ignore_dirs: [],
    input: [],
    log_file: Some(
        "/dev/stdout",
    ),
}
04:41:37 [INFO] Ignoring canonicalized {}

New

More verbose, but I think it's better suited for a log that should provide most information.

[2026-02-06 05:41:32.146 +01:00 INFO src/main.rs:55] dua options=Args {
    command: None,
    threads: 3,
    format: Metric,
    apparent_size: false,
    count_hard_links: false,
    stay_on_filesystem: false,
    ignore_dirs: [],
    input: [],
    log_file: Some(
        "/dev/stdout",
    ),
}
[2026-02-06 05:41:32.154 +01:00 INFO src/common.rs:253] Ignoring canonicalized {}