fix(parquet): skip empty data pages in add_data_page

[adriangb]

Which issue does this PR close?

• Closes Writing a BOOLEAN column with content-defined chunking panics with "RLE value encoder is not initialized" #10929.

Rationale for this change

GenericColumnWriter::add_data_page flushes the encoder unconditionally. Its two neighbouring call sites already avoid calling it with an empty page (should_add_data_page returns false at zero buffered values, and dict_fallback / flush_data_pages test num_buffered_values > 0), but content-defined chunking does not:

// Add a page break after each chunk except the last
if i + 1 < num_chunks {
    match &mut self.writer {
        ArrowColumnWriterImpl::Column(c) => c.add_data_page()?,
        ArrowColumnWriterImpl::ByteArray(c) => c.add_data_page()?,
    }
}

Writing the chunk can already have flushed the page, when the chunk's own values reach data_page_size_limit or data_page_row_count_limit exactly at the chunk boundary. The forced break then flushes a page with nothing buffered.

For a BOOLEAN column that panics. RleValueEncoder creates its inner encoder lazily on the first put and flush_buffer does .take().expect("RLE value encoder is not initialized"), so flushing before any put panics. BOOLEAN resolves to RleValueEncoder under WriterVersion::PARQUET_2_0, or when Encoding::RLE is set explicitly.

For other encodings it does not panic but writes a data page holding zero values.

This is reachable from the public API: WriterPropertiesBuilder::set_content_defined_chunking plus ArrowWriter. data_page_size_limit smaller than max_chunk_size is a configuration the CdcOptions::max_chunk_size docs explicitly describe as supported.

What changes are included in this PR?

add_data_page returns Ok(()) when page_metrics.num_buffered_values == 0, making a forced page break a no-op when there is nothing to write. This brings it in line with the checks the other call sites already make.

Are these changes tested?

Yes, two regression tests in parquet/src/arrow/arrow_writer/mod.rs, both driving only the public ArrowWriter / WriterProperties API. Both fail on main:

• test_arrow_writer_cdc_boolean_forced_page_break_after_flush writes a BOOLEAN column with CDC and a small data_page_size_limit, and checks the values round-trip. On main it panics with RLE value encoder is not initialized.
• test_arrow_writer_cdc_writes_no_empty_data_pages writes an INT32 column with CDC and data_page_row_count_limit, and asserts no data page reports zero values. On main 121 of 611 pages are empty.

Are there any user-facing changes?

Yes, both are fixes:

• Writing a BOOLEAN column with content-defined chunking no longer panics.
• Files written with content-defined chunking no longer contain zero-value data pages.

No public API change, and no change to files written without content-defined chunking.

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This PR was written by Claude (Anthropic's AI assistant) working with @adriangb. The tests were run and the results reported above are actual.