feat: upgrade datafusion 50→51, arrow/parquet 56→57 (#50)

Update dependency versions for compatibility with runtimedb:
- datafusion: 50.1.0 → 51.0
- arrow: 56.2.0 → 57
- parquet: 56.2.0 → 57

Fix deprecated API usage:
- FileScanConfigBuilder::with_projection → with_projection_indices
- UnionExec::new → UnionExec::try_new

Author: anoop-narang