feat(puffin): support deletion-vector-v1 blob read/write

[zhaoxuan1994]

feat(puffin): support deletion-vector-v1 blob read/write

Add end-to-end support for the deletion-vector-v1 Puffin blob type on top
of the existing PuffinReader/PuffinWriter and RoaringPositionBitmap.

Encoding (puffin/deletion_vector.{h,cc}):

• SerializeDeletionVectorBlob / DeserializeDeletionVectorBlob implement the
  DV blob framing: 4-byte big-endian length, 0xD1D33964 magic, the portable
  Roaring vector, and a trailing big-endian CRC-32. Reads validate the magic
  and checksum.
• MakeDeletionVectorBlob builds a spec-compliant Blob: fields set to the
  row-position metadata column id, snapshot-id/sequence-number = -1, no
  compression, and the required referenced-data-file/cardinality properties.

Writing (data/deletion_vector_writer.{h,cc}):

• DeletionVectorWriter accumulates deleted positions per data file, run-length
  encodes each bitmap before serializing, writes one blob per data file, and
  produces a DataFile per blob carrying content_offset/content_size_in_bytes,
  referenced_data_file and record_count for manifest registration.

Reading (data/delete_loader.cc):

• Implement DeleteLoader::LoadDV: read the blob bytes referenced by
  content_offset/content_size_in_bytes, validate referenced_data_file, the 2GB
  limit and cardinality == record_count, then apply positions to the index.
  This wires DV deletes into DeleteFilter::ComputeAliveRows.

Puffin writer convenience:

• PuffinWriter::Make now fills a default created-by property when the caller
  does not provide one, matching the Java writer.

Behavior matches the Java implementation (BaseDVFileWriter / BaseDeleteLoader /
BitmapPositionDeleteIndex): magic, byte order, CRC coverage, blob fields, RLE
and the read-side validations are all aligned.

Tests:

• DV blob framing round-trip and error cases (bad magic, corrupted CRC,
  truncated blob, size mismatch).
• DeletionVectorWriter -> DeleteLoader write/read round trip and guard cases.
• delete_loader: load DV, referenced-file filtering, cardinality mismatch,
  mixed DV + position-delete loading.
• delete_filter: end-to-end ComputeAliveRows filtering with a real Puffin DV
  file over Arrow FileIO.
• PuffinWriter created-by default and caller-precedence.

Not included (deletion-vector upper layer, follow-up): merging with previously
written DVs (compaction), the bulk delete(PositionDeleteIndex) API, and
per-data-file partition/spec in a single DV file.

[Copilot]

Pull request overview

Adds end-to-end support for Iceberg Puffin deletion-vector-v1 blobs, including framing/validation, write-side generation of DV Puffin files, and read-side application of DVs through DeleteLoader into DeleteFilter row filtering.

Changes:

• Implement deletion-vector-v1 blob framing (length + magic + Roaring portable bytes + CRC32) plus spec-compliant Blob construction helpers.
• Add DeletionVectorWriter to emit one DV blob per referenced data file and return manifest-ready DataFile metadata; wire DV loading into DeleteLoader.
• Extend Puffin writer metadata defaults (created-by) and add comprehensive DV-focused unit tests + build system wiring.

Reviewed changes

Copilot reviewed 17 out of 17 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/iceberg/test/puffin_reader_writer_test.cc	Adds tests verifying default created-by behavior and caller override precedence.
src/iceberg/test/puffin_deletion_vector_test.cc	New tests for DV blob framing (round-trip + corruption cases) and Puffin end-to-end DV read/write.
src/iceberg/test/meson.build	Registers new DV-related test sources/targets in Meson.
src/iceberg/test/deletion_vector_writer_test.cc	New end-to-end tests for DeletionVectorWriter ↔ DeleteLoader DV round trips and option/state guards.
src/iceberg/test/delete_loader_test.cc	Adds DV load tests (load, skip mismatched referenced file, cardinality mismatch, mixed DV + position deletes).
src/iceberg/test/delete_filter_test.cc	Adds ComputeAliveRows DV end-to-end test and updates expected error kinds.
src/iceberg/test/CMakeLists.txt	Registers new DV-related tests in CMake.
src/iceberg/puffin/puffin_writer.cc	Auto-populates created-by property when missing.
src/iceberg/puffin/meson.build	Installs new Puffin DV header in Meson.
src/iceberg/puffin/deletion_vector.h	New public API for DV blob serialize/deserialize + spec-compliant Blob creation.
src/iceberg/puffin/deletion_vector.cc	Implements DV blob framing, magic/CRC validation, and blob construction.
src/iceberg/meson.build	Adds new DV source files to the Meson build.
src/iceberg/data/meson.build	Installs deletion_vector_writer.h in Meson.
src/iceberg/data/deletion_vector_writer.h	New writer API for emitting DV blobs into a Puffin file and returning DataFile metadata.
src/iceberg/data/deletion_vector_writer.cc	Implements DV accumulation per referenced file, optimization, Puffin blob emission, and metadata creation.
src/iceberg/data/delete_loader.cc	Implements DV loading path: reads referenced bytes, validates, deserializes, and applies positions to the index.
src/iceberg/CMakeLists.txt	Adds new DV source files to the CMake build.

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[wgtmac]

The PR description is out of date. It still says previous-delete merging and delete(PositionDeleteIndex) are follow-ups, but this version includes both. Please update the description.

[wgtmac]

Two test comments still read like implementation notes but are on unchanged lines, so I can't leave inline comments there. Please trim the routing note in LoadPositionDeletesFiltersByDataFilePath and the fast-path threshold note in LoadPositionDeletesFastPathHonorsReferencedDataFile.

[wgtmac]

Thanks for working on this! I've slightly polished the API design and extracted some functions so they can be reused by other features (like merging v3 DVs during update).