[PERF]: Fully adopt hybrid scan reader in cudf-polars

To fully adopt the hybrid scan reader we need to dispatch to it for both scan types:

- **SplitScan** (single file, row-group aligned splits): partially done in PR #23677
- **FusedScan** (multi-file reads): not yet implemented. Requires Python bindings for the multi-file hybrid scan reader in pylibcudf (PR #22795).

Note: libcudf may eventually auto-dispatch to the correct single or multi-file reader internally.

Start in cudf-polars scan dispatch for SplitScan and FusedScan, then inspect the pylibcudf multi-file hybrid scan reader bindings described in PR #22795. Compare the existing SplitScan work in PR #23677 and verify that both single-file row-group-aligned and multi-file reads dispatch to hybrid readers; done when both scan types are covered.

Written by the indexing model from the issue text.