[@mantine/hooks] use-intersection: Use the last entry from a batched observer callback

[greymoth-jp]

Follow-up to #8509, which fixed the same issue in use-in-viewport.

useIntersection reads only the first entry from the observer callback:

new IntersectionObserver(([_entry]) => {
  setEntry(_entry);
}, options);

When the callback is delayed across frames (busy main thread, fast scrolling), the browser can queue more than one IntersectionObserverEntry for the observed element and deliver them in a single call. The first entry then holds an older state and the last one holds the current state, so the hook can report a stale entry. This is the same situation #8509 describes for use-in-viewport.

The fix mirrors #8509: read the last entry.

new IntersectionObserver((entries) => {
  setEntry(entries[entries.length - 1]);
}, options);

I left use-resize-observer as it is even though it also reads entries[0]: a ResizeObserver reports the current size of each target once per delivery instead of accumulating one entry per frame, so its first entry is already the latest.

Added a regression test that feeds a mock observer a two-entry batch and checks the hook keeps the last entry. Without the change the test fails because the hook returns the stale first entry.