[Discussion] Add async call to TableFunctionImpl trait

Currently, there is only a sync call method in the trait

```rust
/// A trait for table function implementations
pub trait TableFunctionImpl: Debug + Sync + Send {
/// Create a table provider
fn call(&self, args: &[Expr]) -> Result>;
}
```

It would be helpful if we add an async call method to the trait.

Start by locating the TableFunctionImpl trait and reviewing its existing implementations and call sites. Determine the async API shape and update the relevant coverage so the trait supports asynchronous table-function calls without losing the existing synchronous behavior; done means the design is agreed and the affected tests pass.

Written by the indexing model from the issue text.