feat: add table-aware position delete updates

[wirybeaver]

Summary

• add a table-aware PositionDeleteUpdate API that resolves live data-file spec and partition metadata from the current snapshot
• write and commit Puffin deletion vectors for v3 tables while preserving Parquet position-delete files for v2 tables
• merge existing DVs and file-scoped Parquet position deletes, then supersede rewritten delete entries through RowDelta
• sort v2 position deletes deterministically by file path and position, and clean failed outputs in deterministic path order
• report cleanup deletion failures, retain ownership of undeleted outputs, and retry orphan cleanup before writing new output
• validate referenced data files, reuse output across ordinary commit retries, and make the update terminal without deleting output after CommitStateUnknown

Tracks #916.

Dependencies

Depends on #913, #914, and #915. This draft is stacked on their prerequisite commits and should be reviewed and merged after those PRs.

Test plan

• ./build/src/iceberg/test/data_test — 180 tests passed
• ./build/src/iceberg/test/table_update_test --gtest_filter='RowDeltaTest.*' — 15 tests passed
• build/precommit-venv/bin/pre-commit run --files src/iceberg/data/position_delete_update.cc src/iceberg/test/position_delete_update_test.cc — all hooks passed

Focused coverage includes descending v2 input with physical Parquet row-order verification, v2 file-scoped Parquet delete migration to a merged v3 DV, deterministic failure cleanup, ordinary commit retry reuse, and terminal output ownership after CommitStateUnknown. Cleanup-failure coverage verifies that the deletion failure is appended to the original commit error, ownership is retained for the undeleted path, and a later attempt deletes the retained orphan before writing and committing new output.

Remaining test limitation

The pipeline now opts into ValidateDataFilesExist(...).ValidateDeletedFiles(), and the focused RowDeltaTest validation suite passes. A deterministic PositionDeleteUpdate test that injects a persisted v3 rewrite/removal between DV write and retry validation is not included: the retry/replay boundary is internal to Transaction/RowDelta, and the current catalog mock seam proceeds to another catalog attempt rather than exposing a stable validation hook. Covering that exact interleaving would require broader transaction test infrastructure outside this ticket.