Remove async_trait dependency: async fn in traits is stable since Rust 1.75

[alxmrs]

Problem

Cargo.toml includes async-trait = '0.1' and src/lib.rs uses #[async_trait] on the TableProvider impl for PrunableStreamingTable.

The async_trait proc-macro crate was a workaround before Rust 1.75 (December 2023), which stabilized async fn in traits (RPITIT). The proc-macro generates less efficient code — it heap-allocates a Box<dyn Future> for each async call — whereas native async fn in traits avoids this overhead.

Steps

1. Check whether the DataFusion TableProvider trait definition already uses native async fn (it should in recent versions).
2. If so, remove the #[async_trait] attribute from the PrunableStreamingTable impl.
3. Remove async-trait from Cargo.toml [dependencies].
4. Verify with cargo test that nothing breaks.

Benefit

Reduces dependency count and eliminates unnecessary heap allocations in the async execution path.