Add start delay and complete control

[Armadillidiid]

Summary

This PR adds two features:

1. Start Delay: Optional startDelay prop to ProgressBarProvider
2. Complete Control: Explicit control to stop/complete the progress bar with start and complete functions

Motivation

My primary motivation behind this is to prevent progress bars from appearing for fast route changes. Showing a progress indicator for every route change isn't necessary if the navigation completes in under 300ms (imho)

To achieve this behavior, I needed:

1. A way to delay the progress bar appearance until a certain threshold
2. Explicit control to cancel the progress bar if the route change completes before the delay

In the existing implementation, it only provides a start() function with no way to cancel or complete the progress explicitly.

API Changes

Before

const startProgress = useProgress();
startProgress(); // Only way to control progress

After

const { start, complete } = useProgress();
start();    // Start progress
complete(); // Explicitly complete progress

New Props

<ProgressBarProvider startDelay={300}>
  <ProgressBar className="..." />
</ProgressBarProvider>

Usage

export const Link = ({ children, ...props }) => {
  const pathname = usePathname();
  const initialPathnameRef = useRef(pathname);
  const router = useRouter();
  const progress = useProgress();

  // Watch for route changes and complete progress
  useEffect(() => {
    if (pathname !== initialPathnameRef.current) {
      progress.complete();
    }
  }, [pathname]);

  return (
    <NextLink
      onClick={(e) => {
        onClick?.(e);
        if (isModifiedEvent(e)) return;
        e.preventDefault();
        startTransition(() => {
          const { href, replace, scroll } = props;
          progress.start();
          // @ts-expect-error "Auth type doesn't match"
          const url = typeof href === "string" ? href : formatUrl(href);
          if (replace) {
            router.replace(url, { scroll });
          } else {
            router.push(url, { scroll });
          }
        });
      }}
      {...props}
    >
      {children}
    </NextLink>
  );