[Data] Fix UnboundLocalError when read_parquet with columns and no partitioning (#55820)

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## Why are these changes needed?

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solves. -->

If you call `read_parquet` with `partitioning=None` and non-empty
`columns`, then Ray Data raises a error because of a missing branch.
This PR fixes that issue.

```
Traceback (most recent call last):
  File "/root/lab42_vr/test.py", line 6, in <module>
    ds = ray.data.read_parquet(input_s3_path, partitioning=None, columns=columns)
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/.venv/lib/python3.12/site-packages/ray/data/read_api.py", line 950, in read_parquet
    datasource = ParquetDatasource(
                 ^^^^^^^^^^^^^^^^^^
  File "/root/.venv/lib/python3.12/site-packages/ray/data/_internal/datasource/parquet_datasource.py", line 262, in __init__
    data_columns, partition_columns = _infer_data_and_partition_columns(
                                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/.venv/lib/python3.12/site-packages/ray/data/_internal/datasource/parquet_datasource.py", line 817, in _infer_data_and_partition_columns
    return data_columns, partition_columns
                         ^^^^^^^^^^^^^^^^^
UnboundLocalError: cannot access local variable 'partition_columns' where it is not associated with a value
```

## Related issue number

<!-- For example: "Closes #1234" -->

Fixes #55279

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added a
method in Tune, I've added it in `doc/source/tune/api/` under the
           corresponding `.rst` file.
- [ ] I've made sure the tests are passing. Note that there might be a
few flaky tests, see the recent failures at https://flakey-tests.ray.io/
- Testing Strategy
   - [ ] Unit tests
   - [ ] Release tests
   - [ ] This PR is not tested :(

---------

Signed-off-by: Balaji Veeramani <bveeramani@berkeley.edu>

Author: bveeramani

python/ray/data/_internal/datasource/parquet_datasource.py

@@ -825,4 +825,7 @@ def _infer_data_and_partition_columns(
         partition_columns = [
             column for column in user_specified_columns if column in partitions
         ]
+    else:
+        partition_columns = []
+
     return data_columns, partition_columns

python/ray/data/tests/test_parquet.py

@@ -2223,6 +2223,17 @@ def test_parquet_write_parallel_overwrite(
     assert result.count() == 1000
 
 
+def test_read_parquet_with_none_partitioning_and_columns(tmp_path):
+    # Test for https://github.com/ray-project/ray/issues/55279.
+    table = pa.table({"column": [42]})
+    path = os.path.join(tmp_path, "file.parquet")
+    pq.write_table(table, path)
+
+    ds = ray.data.read_parquet(path, partitioning=None, columns=["column"])
+
+    assert ds.take_all() == [{"column": 42}]
+
+
 if __name__ == "__main__":
     import sys