Add maxRedirects guard to UrlChecker

[leMaur]

What

Adds a maxRedirects guard to UrlChecker to bound redirect-following.

Why

getResponse() followed 301/302/307/308 redirects recursively with no depth cap and no cycle guard — a redirect loop could recurse until PHP hit its memory/stack limit. The recursive hop also silently dropped the caller's userAgent/connectTimeout/timeout.

Changes

• New public const UrlChecker::DEFAULT_MAX_REDIRECTS = 5 (untyped, to preserve the package's php: ^8.1 support — typed class constants are 8.3+).
• check() gains a trailing, backward-compatible ?int $maxRedirects = null parameter. maxRedirects: 0 returns the redirect response without following it.
• getResponse() threads a redirectsLeft budget through the recursion, stops once exhausted (returning the last 3xx response), and now preserves the caller's user-agent and timeouts on every hop.
• README documents the redirect behavior and the new parameter.

Tests

5 new Pest cases: each of 301/302/307/308 must terminate (in fake mode every hop re-serves the same response, so without the guard the suite would hang — a genuine regression test), plus a maxRedirects: 0 no-follow case.

Local gates: pest 17 pass / 29 assertions, phpstan analyse no errors, pint --test passed.