Fix #4788 — repopulate mt_natural_key on projection rebuild (ported to V8)

[ytqsl]

• test: repro rebuild projection with natural key

• fix: query by natural key

• updated file name

• Fix Natural keys table is not populated when rebuilding a snapshot #4788: rebuild a [NaturalKey] aggregate also rebuilds the mt_natural_key lookup table

The natural-keys lookup table (mt_natural_key_{aggregate}) is maintained by NaturalKeyProjection, an auto-registered inline projection whose ApplyAsync iterates the StreamActions queued during the current SaveChanges and writes ON CONFLICT upserts per matching event. That dispatch fires correctly on the normal append path but the async-daemon rebuild path appends no streams — it replays already-persisted events from mt_events through the projection's aggregator and stores the rebuilt snapshots, so the inline projection chain is never given anything to iterate. Net effect: after rebuild the parent projection's documents are repopulated, but the mt_natural_key table stays exactly as teardown left it (empty), and any FetchLatest<T, TNaturalKey> afterwards misses.

Fix — two new hooks in Marten, no JasperFx changes required (the existing abstractions — IAggregateProjection.NaturalKeyDefinition, EventRange.Events on every rebuild page, and ProjectionBatch.SessionForTenant routing writes into the batch's work-tracker — already give Marten everything it needs):

1. teardownProjectionStorage now also wipes the natural-key table when the source projection carries a NaturalKeyDefinition, so the rebuild starts from a clean slate (mirrors the doc-table TRUNCATE).

2. StartProjectionBatchAsync, in Rebuild mode, looks up the source by range.ShardName.Name and — when it has a NaturalKeyDefinition — feeds range.Events through a new NaturalKeyProjection.QueueUpsertsForEvents method per tenant. The IDocumentOperations comes from projectionBatch.SessionForTenant(...) which returns a ProjectionDocumentSession whose ISessionWorkTracker IS the ProjectionUpdateBatch — so the upserts flush inside the same transaction as the rebuilt snapshots, not the bare session's unit-of-work (which the batch's ExecuteAsync never touches).

NaturalKeyProjection refactor: extracted queueUpsertSql to take (streamId, streamKey, tenantId, innerValue) instead of a StreamAction so the inline path (StreamAction-driven) and the rebuild path (IEvent-driven) share the SQL builder. ApplyAsync behavior is byte-for-byte unchanged.

Test: ytqsl's Bug_4788_natrual_key_table_not_populated_on_rebuild repro (authored in commits 27ecadd / 12f16db / 6322a63 on this branch) now passes. Broader regression sweep on net10: 34/34 existing natural-key tests

• 8/8 EventSourcingTests rebuild tests + 31/31 DaemonTests rebuild tests all green.

Closes #4788
Supersedes #4789

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