feat(table): drop dangling equality deletes during RewriteDataFiles

[laskoviymishka]

Closes #946.

Sustained CDC workloads (Postgres → Iceberg replication, ~one snapshot per few seconds with one eq-delete per UPDATE/DELETE) accumulate equality-delete files in every snapshot's manifests forever. After compaction, every preexisting eq-delete is provably dead — no surviving applicable data file has seq < eq-delete.seq — but the old RewriteDataFiles only removed position deletes, leaving eq-deletes in place. Manifest fanout grew linearly with the CDC duration.

This change adds three pieces:

1. table/compaction.DecideDeadEqualityDeletes — a pure predicate that exactly matches the v2 reader (table/scanner.go matchEqualityDeletesToData): E applies to D iff E.seq > D.seq AND (either side has empty partition OR partition tuples match). SpecID is intentionally NOT in the predicate — using it would silently drop eq-deletes the reader still applies under partition-spec evolution.

2. table/compaction.CollectDeadEqualityDeletes — walks the snapshot's manifests via the existing public Snapshot.Manifests + FetchEntries APIs, builds a SurvivorSurvey, and returns the dead set. Two-pass design: skip the data-manifest walk if there are no eq-delete candidates.

3. table.RewriteDataFilesOptions.ExtraDeleteFilesToRemove — a new field on the options struct that the executor passes through to ReplaceFiles. The caller (cmd/iceberg/compact.go or any library user) computes dead eq-deletes via CollectDeadEqualityDeletes against the same snapshot and threads them in. The executor itself is policy-free.

The CLI gains a --preserve-dead-equality-deletes flag (default off, i.e., cleanup is on by default — recommended for sustained CDC).

The RewriteDataFiles signature collapses (partialProgress, snapshotProps, opts...) into a single RewriteDataFilesOptions struct. RewriteResult splits RemovedDeleteFiles into RemovedPositionDeleteFiles + RemovedEqualityDeleteFiles for observability.

Tests:

• table/compaction/eq_delete_decision_test.go pins the predicate against the scanner's rule across mixed-partition / cross-spec / boundary cases.
• table/compaction/cdc_stress_test.go runs 80 CDC cycles (81 data files + 80 eq-deletes pre-compaction → 1 data file + 0 eq-deletes post). Skipped under -short.
• table/rewrite_data_files_test.go covers full-rewrite drops, partial-rewrite preserves, partial-progress preserves (per-group cleanup is a follow-up), and the CLI opt-out path.