Optional browser-based auth_token extractor (interest check)

[feder-cr]

hey, before building it i wanted to check if there'd be interest in an optional helper that performs the X login flow in a real stealth browser once, then dumps cookies to a file that twikit's existing load_cookies can read directly. no change to twikit's HTTP core.

motivation: ToProtectYourAccount.md already recommends save_cookies / load_cookies to avoid repeated login calls. the first login still has to happen somewhere though, and increasingly X's login flow requires JS challenges (Castle Token, ondemand.s.js fingerprinting) that pure HTTP can't pass cleanly. relevant open PRs touching this surface: #324 #393 #410.

the helper would wrap feder-cr/invisible_playwright, which drives a patched Firefox 150 (feder-cr/invisible_firefox, MPL-2, same license as Firefox upstream, fingerprint patches at the C++ source level so no JS shims to detect). optional dependency, only loaded when the helper is imported. used as login_to_cookies(username, email, password, output='cookies.json') then the usual twikit path with client.load_cookies('cookies.json'). issues against the helper route to feder-cr/invisible_playwright.

also opened a draft PR #427 with a proposal doc at the repo root so the idea has somewhere concrete to land.