The previous implementation queried https://archive.org/wayback/available,
parsed its JSON response, and extracted the closest snapshot URL. That API
is heavily rate-limited and frequently returns empty 'archived_snapshots'
for pages that are clearly archived, leading to false 'no suggestion'
results.

Instead, request https://web.archive.org/web/<url> directly. Wayback
resolves the latest snapshot server-side and either:

- responds 302 with a Location pointing at the actual timestamped
  snapshot (e.g. /web/20260530081255/http://example.com/). We read the
  Location header directly, without following the redirect, so users see
  the capture date in the suggested link without downloading the archived
  page.
- responds 404 when no snapshot exists, in which case we return None so
  lychee doesn't suggest a dead-end 'page not archived' link.

Note: the timestamp is omitted from the request URL. A '0' timestamp
would resolve to the *oldest* snapshot, whereas omitting it yields the
latest capture.

Other improvements:

- Share a single LazyLock<reqwest::Client> across all suggestion lookups
  so they reuse the connection pool, TLS session cache, and DNS resolver.
  The client uses redirect::Policy::none() since we read Location ourselves.
- Drop the timeout parameter from Archive::get_archive_snapshot. With a
  shared static client, baking a sensible default (20s) is simpler than
  threading the value through callers. This is a breaking change to the
  public lychee-lib API.
- Drop the InternetArchiveResponse / ArchivedSnapshots / Closest structs
  and the custom StatusCode deserializer.
- Replace the wiremock-based test, the API-docs scrape, and the two
  ignored real-network tests with two deterministic real-network tests
  covering the 302-with-Location and 404-becomes-None cases. The
  'unknown URL' test still tolerates 503s as transient.

The two real-network tests each ran on their own #[tokio::test] runtime while sharing the process-wide static reqwest::Client. The client's connection-pool tasks bind to whichever runtime initializes it first, so the sibling test could reuse a pooled connection whose runtime was already torn down, failing intermittently with 'runtime dropped the dispatch task' (DispatchGone).

Run both cases in a single test (one runtime) to keep the shared-client design intact while making the tests deterministic.