Stop the browser on a redirect when followRedirects(false)

[kbond]

Draft: this branch is based on #53, so the diff includes it. I will rebase once that lands.

followRedirects(false) currently does nothing. The flag is inherited from AbstractBrowser and isFollowingRedirects() reports it correctly, but the route handler follows every 3xx regardless.

This makes it stop instead: the 3xx is fulfilled as a 200 with no Location and an empty body, so the browser parks on the url that redirected while getLastSymfonyResponse() keeps the real status and Location for the caller to inspect. The body has to be dropped because a RedirectResponse carries a <meta http-equiv="refresh"> that navigates whatever the status says.

followRedirect() then steps a stopped redirect one hop at a time. fetch redirects keep their client-side replay: followRedirects() is about where the test client navigates, not what application JS asked fetch() to do.

This is what zenstruck/browser needs for interceptRedirects(), followRedirect(), assertRedirected(), assertRedirectedTo() and clickAndIntercept(), whose existing KernelBrowser implementations already call exactly followRedirects(false).