Add relation view generations for cache invalidation

[justinjoy]

Discovery context

Architect/Critic review of #1435 found that materialization-cache pinning can be implemented independently, but relation-view correctness needs a separate generation contract. Arrangement bucket generations do not cover same-row-count mutation, row permutation, compaction, rollback, COW transitions, or worker-copy ownership.

Scope

• Add explicit rowset/order and storage-buffer generations to col_rel_t.
• Increment the appropriate generation on append, permutation, compaction, rollback, COW unshare, and replacement-buffer publication.
• Store source generations in materialization, filtered, sorted, and differential cache entries where applicable.
• Reject stale views and force rebuild/miss even when nrows is unchanged.
• Define worker clone/reset behavior for every generation field and validate teardown under sanitizers.

Acceptance criteria

• Same-row-count mutation, permutation, retraction/rollback, compaction, and COW transitions invalidate the correct cached view.
• Cache lookup validates source generations rather than relying only on row count or arrangement bucket generation.
• Worker create/destroy with populated relation views has no stale-view, double-free, or use-after-free failure under ASan/UBSan.
• Existing arrangement, filtered, differential, sorted, materialization, retraction, compaction, and worker tests remain green.
• No public API/ABI, spill implementation, or suspended-reader subsystem is added.

Dependency

Depends on the materialization-cache pin/deferred-destruction unit in #1435 and feeds #1371, #1372, #1382, and #1383.

[justinjoy]

Architect/Critic review found that the full cache-consumer generation change is not one safe atomic unit. The first prerequisite is now tracked in #1441: relation identity, view/storage generation semantics, complete mutation instrumentation, overflow policy, rollback freshness, and worker-copy behavior.

#1441 deliberately excludes cache lookup changes. After it is implemented and validated, #1438 will consume the generation contract for materialization, filtered, sorted, primary, and differential views.

[justinjoy]

Implementation PR: #1443

#1438 cache consumers now validate relation identity, view generation, and storage generation instead of relying on nrows/content-prefix freshness. Materialization, filtered, primary, filtered-arrangement, sorted, and differential consumers rebuild on mismatch; worker clones do not inherit coordinator snapshots.

Validation: normal and ASan/UBSan cache/arrangement regressions 15/15; post-format focused cache suites 10/10 in both builds; clang-tidy, ABI/public API, threading_doc, and diff checks passed.

#1443 is stacked on #1442. Lifetime/pinning remains in #1384/#1435. The issue remains open until the stacked PR chain is merged.