Remove partitioned table read restriction in TableRead

[luoyuxia]

Parent Issue

Part of #124 (support partitioned table)
Depends on #128 (fix TableScan partition paths)

Background

TableRead::to_arrow() explicitly rejects partitioned tables:

// read_builder.rs:88-95
if !self.table.schema.partition_keys().is_empty() {
    return Err(Error::Unsupported {
        message: format!(
            "Reading partitioned tables is not yet supported. Partition keys: {:?}",
            self.table.schema.partition_keys()
        ),
    });
}

Once TableScan generates correct partition paths (#128), the ArrowReader will be able to read data files under partition directories without additional changes (since it reads from the bucket_path in DataSplit).

What needs to be done

1. Remove the partition key check in TableRead::to_arrow() (lines 88-95 of read_builder.rs)
2. Verify ArrowReader works with the corrected paths — it reads {bucket_path}/{file_name}, so as long as bucket_path is correct, no ArrowReader changes should be needed

Affected files

• crates/paimon/src/table/read_builder.rs — TableRead::to_arrow() method

[luoyuxia]

Merged into a combined issue with #128 and #130