Function watch 

pub fn watch(
    dir: &Path,
    on_change: Option<ChangeHandler>,
    debounce: Option<Duration>,
) -> Result<WatchHandle>

Spawn a recursive debounced watcher on dir using the default WatchConfig (skips conventional noise paths — .git/, target/, node_modules/, etc.).

Returns a handle whose Drop impl tears the watcher down. Errors surface synchronously if the path is not a directory or the platform watcher refuses to register.

For control over the skip set, use watch_with_config.