feat: add deletion vector compaction planner

[wirybeaver]

Summary

• add a snapshot-bound, metadata-only CompactionPlanner without rewrite execution
• select small files and files with qualifying, deduplicated file-scoped position-delete pressure; equality and partition-scoped deletes are excluded
• reject duplicate data-file scan tasks before candidate counting and require qualifying delete pressure for oversized files
• validate configuration, non-negative source snapshot IDs, and file metadata; reject missing partition spec IDs and invalid DV cardinality; cap position-delete cardinality and return checked-arithmetic errors
• group null- and NaN-containing partitions with canonical Iceberg equality semantics and emit deterministic partition/file order
• compare near-INT64_MAX size and delete-ratio thresholds without lossy integer-to-double conversion
• use deterministic best-fit-decreasing packing to shape partition groups by target_file_size_bytes

API for Ticket 08

• planning requires CompactionPlanner::Plan(int64_t source_snapshot_id, scan_tasks, config)
• negative source snapshot IDs are rejected
• CompactionPlan::source_snapshot_id records the snapshot used to produce the scan tasks
• an executor must validate that source snapshot before rewriting, so a stale plan cannot silently resurrect rows deleted after planning

This PR is stacked on #913 and #915. Until those dependencies merge, it contains their prerequisite commits; review commit 56ed503 for Ticket 07 itself. This replaces Ticket 07 commit 03990086 (which had already replaced f05db6b), and Ticket 08 must synchronize to 56ed50369dcdfedd7af5962493ecfc33af0420af.

Part of #916.

Test Plan

• GCC 14 build: cmake --build build --target compaction_planner_test util_test -j2
• GCC 14 tests: ctest --test-dir build -R "^(compaction_planner_test|util_test)$" --output-on-failure (2/2 passed)
• planner tests (18 total) cover config and threshold boundaries, zero-threshold semantics, snapshot binding and negative IDs, duplicate data-file tasks, null and canonical NaN partitions, missing spec IDs, deterministic ordering, mixed delete kinds, delete deduplication/DV ranges, cardinality capping and validation, checked overflow, exact near-INT64_MAX comparisons, oversized files, partition isolation, small files, target-sized grouping, and best-fit 60,60,40,40 packing
• /home/user/.cache/uv/archive-v0/1n0bbgciCQ9iE9BH/bin/pre-commit run --all-files (all hooks passed)
• git diff --check (passed)

Revert Plan

Revert commit 56ed50369dcdfedd7af5962493ecfc33af0420af and restore the prior Ticket 07 dependency in downstream branches.