Async API for RestCatalog

### Feature Request / Improvement

RestCatalog currently uses synchronous HTTP calls, while most catalog operations are network io-bound. Native async support would help async consumers and high-concurrency use cases in general.

We could introduce a separate AsyncRestCatalog, preserving the existing synchronous API.

asyncio.to_thread()/running in a dedicated executor is a possible workaround but doesn't give the same benefits as native support as we'd still have the limitations of the sync client (one worker thread per in-flight request being the most annoying in this case).

We can start small without necessarily the full ops coverage, wdyt?

Parti dall’implementazione esistente di RestCatalog e mappa quali operazioni del catalogo utilizzano attualmente chiamate HTTP sincrone. Definisci l’ambito iniziale di AsyncRestCatalog mantenendo l’API sincrona; l’issue lascia aperti la copertura esatta delle operazioni e l’approccio di validazione.

Scritto dal modello di indicizzazione a partire dal testo della issue.