[Fix][CachedRouting] Persist route cache in local file store

[agissept]

Summary

CachedRouting\Router::cache()/clearCache() resolved the container's default cache store — which in production is Redis. Routes are loaded during application boot (Foundation/start.php → app/routes.php → Route::cache()), so every web request and artisan command — including queue:work — issued a Redis GET at boot. When Redis was unreachable, boot itself failed:

Predis\Connection\ConnectionException: Connection refused [tcp://127.0.0.1:6390]
  ... Illuminate\Cache\RedisStore->get('routes.cache.v2...')
  ... Illuminate\CachedRouting\Router->cache(...)   (api_routes.php:3)
  ... require routes.php                             (start.php)
  ... Illuminate\Console\Application::make() → $app->boot()  (artisan)

Route cache is a build-time artifact, deterministic per release — it belongs on local disk, exactly like modern Laravel's file-based route cache (bootstrap/cache/routes-v7.php, loaded via require, never a network store).

What it changes

• Router::cache() / clearCache() now use the file cache driver via a small getRouteCacher() helper, instead of the default (Redis) store. Booting no longer depends on a networked cache.
• Invalidation is unchanged — the cache key still embeds the route file filemtime, so a new deploy auto-rebuilds on first hit.
• Tests run against the file store (temp dir + cleanup) to exercise the real path.

No public API change; Route::cache(__FILE__, ...) call sites are untouched.