Add hybrid scan multifile single-step materializers

[mhaseeb123]

Description

Contributes to #22583

This PR adds single-step column materialization APIs for the multifile hybrid scan reader

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR extends the experimental hybrid_scan_multifile API by adding four public methods for row mask construction and column materialization from multi-file Parquet sources. Implementations delegate to the underlying implementation, while test utilities provide shared helpers for multifile setup, and new test cases validate row masking and column materialization behavior.

Changes

Hybrid Scan Multifile API Extension

Layer / File(s)	Summary
Public API declarations and documentation cpp/include/cudf/io/experimental/hybrid_scan_multifile.hpp, cpp/src/io/parquet/experimental/hybrid_scan_impl.hpp	Four new public methods declared: build_all_true_row_mask, build_row_mask_with_page_index_stats, all_column_chunks_byte_ranges, and materialize_all_columns. Doxygen references retargeted to multifile API variants.
Public API method implementations cpp/src/io/parquet/experimental/hybrid_scan_multifile.cpp	Four methods implemented as forwarding wrappers that delegate row-group indices, options, and stream/memory parameters to underlying _impl and return results.
Test utilities and shared helpers cpp/tests/io/experimental/hybrid_scan_common.hpp, cpp/tests/io/experimental/hybrid_scan_multifile_common.hpp, cpp/tests/io/experimental/hybrid_scan_test.cpp, cpp/tests/CMakeLists.txt	make_list_str_column helper added/moved to common header; new multifile_inputs struct and build_source_info/setup_page_indexes helpers introduced for test data management; duplicate helper removed from a test file; new test source registered in CMake.
Filter tests refactoring and row mask test suite cpp/tests/io/experimental/hybrid_scan_multifile_filters_test.cpp	Existing tests refactored to use shared utilities; new host_row_mask_data and make_scalar helpers added; BuildAllTrueRowMask test validates mask properties; typed test suite HybridScanMultifilePageIndexRowMaskTest validates row mask filtering with page-index statistics across multiple filter expressions and error handling.
Column materialization test suite cpp/tests/io/experimental/hybrid_scan_multifile_test.cpp	Adds tests for materialize_all_columns covering lists, list-of-strings, and struct column types; helper groups and flattens per-row-group byte ranges for device input.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• rapidsai/cudf#22613: Related multifile page-index fetching helpers used by page-index row-mask tests.
• rapidsai/cudf#22616: Introduces base hybrid_scan_multifile infrastructure that this PR extends.

Suggested labels

feature request, 4 - Needs Review, non-breaking

Suggested reviewers

• lamarrr
• shrshi
• qbacpey
• PointKernel
• bdice

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 7.14% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly and specifically describes the main change: adding single-step materializers for the multifile hybrid scan reader.
Description check	✅ Passed	The pull request description is clearly related to the changeset, describing the addition of single-step column materialization APIs for the multifile hybrid scan reader.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[vyasr]

CMake approval (didn't look at the C++)

[mhaseeb123]

/merge