feat: add table-aware position delete updates

[wirybeaver]

Summary

Deliver table-aware end-to-end position deletion: write v3 Puffin DVs, preserve the v2 Parquet path, merge prior deletes, supersede old entries, and commit through RowDelta.

• resolve each target's live partition/spec and keep minimal scan consistency checks with existing sequence-number fail-fast behavior

• retain conflict validation, unknown-commit output preservation, and retry-safe cleanup; define missing-file deletion as idempotent at the shared FileIO seam

• verify actual surviving Parquet rows after two commits and a fresh table load, including partition evolution

• exercise a real concurrent data-file removal during commit/retry

• resolve requested files lazily, reuse the existing delete-write result, and centralize commit-result handling with a small shared cleanup helper

• consolidate duplicate routing/order tests and reuse the existing retry test harness without weakening conflict or unknown-commit coverage

DV-PR-1 in #916. Supersedes the standalone applicability work in #915. Based directly on main at 3c5715c; no dependency on #913, #914, or #915. Full Puffin footer hardening and standalone fixtures are deliberately excluded.

Test plan

GCC 14 focused checks on the four-feature integration tree based on 3c5715c; the final changed branch sources were verified to match the tested tree.

• data_test --gtest_filter='*PositionDeleteUpdateTest*:*PositionDeleteV3Test*': 16 passed

Includes actual Parquet row survival after two commits/reload, partition evolution, a persisted concurrent removal, cleanup/retry, unknown commit ownership, and v2 physical delete ordering.

• Repository pre-commit checks and git diff --check: passed