Add a `RLE` array exporter to duckdb

[joseph-isaacs]

Currently we can only export RunEnd to duckdb add a RLE exporter which is actually quicker to export to a duckdb dict.

    let array = match array.try_downcast::<RunEnd>() {
        Ok(array) => return run_end::new_exporter_with_flatten(array, cache, ctx, flatten),
        Err(array) => array,
    };

+   let array = match array.try_downcast::<RLE>() {
+       Ok(array) => return rle::new_exporter(array, cache, ctx),
+       Err(array) => array,
+   };