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?

从现有的 RestCatalog 实现开始，梳理当前哪些 catalog 操作使用同步 HTTP 调用。在保留同步 API 的同时，定义 AsyncRestCatalog 的初始范围；该 issue 未确定具体的操作覆盖范围和验证方式。

由索引模型根据 Issue 内容生成。