Attach runtime before calling scan for foreign table provider

**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**

In the table provider for `lance` in the `scan` method I sometimes have to do a small amount of I/O to load dataset metadata if the metadata is not already in the cache. The `scan` method is async so I assume this is ok. However, I use `spawn_blocking` to trigger this I/O and it fails because the runtime is not active.

**Describe the solution you'd like**

The runtime should be attached before calling `scan`.

**Describe alternatives you've considered**

Currently I work around this by forcing the metadata to be cached before creating the table provider but this is inconvenient.

**Additional context**

Can provide additional details (stack traces, lance reproducers, etc.) on request.

從表格提供者的非同步 `scan` 進入點以及 issue 中描述的 `spawn_blocking` 路徑開始。重現一次 Lance 中繼資料快取未命中，追蹤 runtime 相對於 `scan` 的附加時機，並確認快取未命中路徑能在不發生 runtime 錯誤的情況下完成。

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