better-route: rate limiting

Use a fixed-window limiter with an atomic backend. Pick the backend from deployment capabilities; do not silently fall back from an atomic store to a racy read/modify/write.

Persistent object cache

use BetterRoute\Middleware\RateLimit\RateLimitMiddleware;
use BetterRoute\Middleware\RateLimit\WpObjectCacheRateLimiter;

$rateLimit = new RateLimitMiddleware(
    limiter: new WpObjectCacheRateLimiter(group: 'myapp_rate_limit'),
    limit: 60,
    windowSeconds: 60,
);