feat(design-system): add infiniteScroll to DsTable to handle scroll pagination [AR-62554]

[iromanchuk-dn]

Problem

Consumers of the virtualized DsTable had to hand-roll infinite scroll on every page:

• Listen to onScroll, compute bottomOffset, compare to a threshold, gate on isFetching/hasMore.
• Get scroll position from a useEffect on mount and after each fetch to handle the "initial data is shorter than the viewport, so no scrollbar ever appears" footgun. It is not possible today and a related bug was reported.
• Re-implement this ~30-line snippet for every list — error-prone, easy to forget the auto-fill check, and leaks scroll-math into product code that should only care about fetching.

Solution

Encapsulate viewport/scroll detection inside DsTable. Consumers keep ownership of fetching, pagination state, and retry; the Table owns when to ask for more.

New prop

<DsTable
  virtualized
  data={rows}
  columns={columns}
  infiniteScroll={{
    hasMore,          // required
    isLoadingMore,    // default: false
    onLoadMore,       // required; sync or () => Promise<unknown>
    thresholdPx,      // default: 500
    autoFill,         // default: true
  }}
/>

• Presence of infiniteScroll = feature on. No enabled flag.
• hasMore: false is the runtime off-switch (end of data, error, pause).
• autoFill: true keeps requesting pages until the viewport is actually scrollable — fixes the "short first page" footgun by default.
• onLoadMore accepts (() => void) | (() => Promise<unknown>), so React Query's fetchNextPage can be passed directly without a wrapper.
• Existing onScroll prop continues to work independently for analytics / scroll indicators.

Implementation

• New useInfiniteScroll hook (use-infinite-scroll.ts) owns threshold detection, the auto-fill loop, and an in-flight latch.
• Reentrancy guard: latch is set the moment onLoadMore fires; cleared when isLoadingMore transitions to true. Closes the 1–2 frame gap before the consumer's loading flag propagates without forcing Promise semantics on the API.
• Wired into the virtualizer's existing onChange for scroll-driven triggers and a useEffect on rows.length for mount / data-append / auto-fill. The isNearBottom check is gated on actual scrollability so it doesn't false-fire when content is shorter than the viewport.

Migration & coverage

• Existing VirtualizedSelectable and VirtualizedExpandable stories migrated off the manual fetchMoreOnBottomReached + getScrollPosition plumbing.
• New InfiniteScroll (5-row initial page) stories anchor the API.
• New ds-table-infinite-scroll.browser.test.tsx covers: threshold trigger, hasMore: false guard, isLoadingMore: true guard, auto-fill on mount (both true and false), and the latch regression.

Test plan

• pnpm eslint packages/design-system/src/components/ds-table/
• pnpm --filter @drivenets/design-system typecheck
• pnpm --filter @drivenets/design-system test src/components/ds-table/__tests__/ --run
• Verify all four virtualized stories in Storybook (existing two + two new) trigger paging on scroll and auto-fill on short initial pages.

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[vpolessky-dn]

Tests cover “rapid scroll before loading flag propagates”, but there’s no test for the valid API case where onLoadMore is sync (or async without isLoadingMore) and should still allow repeated pagination cycles.

[iromanchuk-dn]

I removed latch behavior, it's overcomplicates things.