better-route: atomic idempotency

Use atomic idempotency for writes whose side effect must not execute twice under concurrent retries. It reserves before invoking the handler; classic IdempotencyMiddleware only stores after completion.

Production setup

use BetterRoute\Middleware\Write\AtomicIdempotencyMiddleware;
use BetterRoute\Middleware\Write\WpdbAtomicIdempotencyStore;

register_activation_hook(__FILE__, static function (): void {
    (new WpdbAtomicIdempotencyStore())->installSchema();
});

$atomic = new AtomicIdempotencyMiddleware(
    store: new WpdbAtomicIdempotencyStore(),
    ttlSeconds: 86400,
    requireKey: true,
);