refactor: optimize many-to-many relation loading for audit tracking - #173
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Summary Updating an entity that has several many-to-many relations flagged with enableAuditTracking: true can time out (canceling statement due to statement timeout) instead of completing, once each relation has more than a small handful of related rows. Confirmed in production on PUT /api/country/:id (Country has 7 audit-tracked many-to-many relations: product, section, pageSeoMetadara, seo, Blogs, falconBanner, testimonial).
Root cause CRUDService.prepareManyToManyAuditSnapshot() (crud.service.ts) and AuditSubscriber.prepareManyToManyAuditUpdateSnapshot() (audit.subscriber.ts) each build the audit before/after snapshot with a single repo.findOne({ relations: {...} }) call that includes every audit-tracked relation at once. TypeORM compiles that into one SQL query with a LEFT JOIN per relation. Joining N sibling many-to-many relations off the same row in a single query produces the cartesian product of their row counts, not the sum — e.g. 7 relations at ~150 rows each yields up to 150⁷ (~1.7 × 10¹⁵) result rows for a single query, which blows past any reasonable statement timeout even though no individual relation holds "a lot" of data.