fix: forward write_options when write_parquet receives ParquetWriterOptions

[Rodrigo-Palma]

Which issue does this PR close?

Closes #1760.

Rationale for this change

DataFrame.write_parquet accepts write_options, documents it and declares it in the @overload for the ParquetWriterOptions form, but that branch delegates without forwarding it:

if isinstance(compression, ParquetWriterOptions):
    if compression_level is not None:
        msg = "compression_level should be None when using ParquetWriterOptions"
        raise ValueError(msg)
    self.write_parquet_with_options(path, compression)   # write_options dropped
    return

write_parquet_with_options(path, options, write_options=None) takes the parameter, so everything in DataFrameWriteOptions (partition_by, single_file_output, insert_operation, sort_by) was silently ignored for that one spelling. Measured with the same DataFrameWriteOptions(partition_by="part") in all three calls:

write_parquet(path, ParquetWriterOptions(), write_options=wo)        ['IDuOjvMa3pdEDotb_0.parquet']
write_parquet_with_options(path, ParquetWriterOptions(), ...=wo)     ['part=a', 'part=b']
write_parquet(path, "zstd", write_options=wo)                        ['part=a', 'part=b']

Only the ParquetWriterOptions branch loses the Hive partitioning, with no error and no warning, so the files just land in the wrong layout.

The branch came in ef62fa8 (#1169) while write_options was added earlier in #857, so the new delegation path was written without carrying the existing parameter over. Note that the same if refuses compression_level with an explicit ValueError: arguments genuinely incompatible with this branch get rejected on purpose, and write_options was not rejected, only forgotten.

What changes are included in this PR?

One line: write_options is passed through to write_parquet_with_options. Plus a regression test, test_write_parquet_writer_options_keeps_write_options, next to test_write_parquet.

• Without the change: AssertionError: assert ['9UNQ0jX8PC8GFZxz_0.parquet'] == ['part=a', 'part=b']
• With it: 1 passed

python/tests/test_dataframe.py: 327 passed with the change against 326 on a clean tree, with the same 4 pre-existing errors in both runs (test_logical_plan, test_optimized_logical_plan, test_execution_plan, test_async_iteration_of_df), so the delta is exactly the new test. ruff 0.15.1 check and ruff format --check are clean on both files.

Measurement caveat: I ran the Python layer of this branch against the published datafusion 54.0.0 wheel rather than a locally built _internal, so the Rust side is the released one. The block being changed is byte-identical between that wheel and main, which I verified by diffing it, so the behaviour shown above is the behaviour on main.

Are there any user-facing changes?

Yes, in the sense that write_options now takes effect for this call shape, which is what the signature, the docstring and the overload already promise. No API change: no signature, name or default is touched.