Closes WOOMOB-1297

Summary

This PR introduces POSCatalogIncrementalSyncService for incremental sync by only fetching products and variations modified since the last full/incremental sync. Only the remote sync is implemented in this PR, persistence is in #16106 to make reviews easier.

Key Changes

• POSCatalogIncrementalSyncService: New service implementing incremental sync logic with per-site sync date tracking. The last incremental sync date will be persisted in a future task WOOMOB-1289
• BatchedRequestLoader: Generic utility extracted from existing sync services for reusable paginated data loading

Steps to reproduce

Just CI is sufficient, as the full/incremental services aren't integrated with the app yet.

Testing information

I tested that full sync worked as before, and incremental sync worked after a full sync for a big site:

Task {
   do {
        let date = Date()
        let catalog = try await syncService.startFullSync(for: siteID)
        print("Full sync completed with \(catalog.products.count) products and \(catalog.variations.count) variations for siteID \(siteID)")

        try await incrementalSyncService.startIncrementalSync(for: siteID, lastFullSyncDate: date)
        print("Incremental sync completed")
    } catch {
        print("Full sync failed for siteID \(siteID) with error: \(error)")
    }
}

If the full sync integration is merged, I will test the incremental sync with debug code after full sync integration is in trunk.

• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.