feat: allow TableScans of non-federated sources

[phillipleblanc]

Relaxes get_table_source called in get_federation_provider to allow TableScans of non-federated tables.

The optimizer already handles this case with:

        // Check if this node determines the FederationProvider
        let sole_provider = self.get_federation_provider(plan)?;
        if sole_provider.is_some() {
            return Ok((None, sole_provider)); // <-- Federated TableScans return Some
        }

        // optimize_inputs
        let inputs = plan.inputs();
        if inputs.is_empty() {
            return Ok((None, None)); // <-- Will mark this TableScan as non-federated by returning None
        }