Fix flaky sectionlist-viewability E2E flow on iOS (#59395)

Summary:
`test_e2e_ios_rntester` on `main` keeps failing on `sectionlist-viewability.yml`, with `No visible element found: id: Brownie` on all 5 attempts. It isn't a recent regression: the same flow has failed this way regularly on `main` since at least Oct 8.

**Root cause.** In the horizontal waitForInteraction step, `scrollUntilVisible` scrolls until `Brownie` is centered, with a 60s timeout:

- With `direction: RIGHT`, Maestro (2.6.1, `UiElement.isElementNearScreenCenter`) counts an element as centered only when its center is left of `centerX + width/5`, which is 70% of the screen width. `Brownie` is the **last** item of the list, so its center can never get that far left (it ends at about 85% of the width).
- When the element is visible but not centered, Maestro spends `maxRetryCenterCount` (4+1) more swipes before falling back to the plain `visibilityPercentage` check.
- On CI each swipe moves the list by about one item and takes ~3–4s. In the recorded failure (Release, run 39903033948), scrolling starts at ~104s of the video and only reaches the end of the list at ~162s, about 58s into the 60s budget. The step then times out during the extra centering swipes, even though `Brownie` is fully on screen.

Whether it passes depends on runner speed, so the flow is flaky. `flatlist-viewability.yml` has the same structure but targets `Cheesecake`, the second-to-last item, and it rarely fails.

**Fix.**
- Target `Cheesecake`, like the FlatList flow does. It reaches the center zone, and it's the item the next step asserts on (`output` contains `Cheesecake`).
- Raise the step timeout to 120s, to give the full traverse some headroom.

The Android-only vertical block is unchanged; it passes on Android.

## Changelog:

[INTERNAL] [FIXED] - Fix flaky sectionlist-viewability E2E flow on iOS

Pull Request resolved: #59395

Test Plan:
- Looked through the iOS RNTester E2E jobs of ~225 `main` runs from Oct 8–22. `sectionlist-viewability` is by far the most common hard failure, in both Debug and Release, before and after #58991 switched the selector from text to testID.
- Pulled frames from the failure recording (`e2e_ios_…_report_Release_NewArch`) to confirm the timeline above. The last frame shows the list scrolled to the end, with `Cheesecake` and `Brownie` fully visible and the output showing `Cheesecake, Brownie`.
- I couldn't run Maestro locally because the network policy on my machine blocks Maestro's localhost connection to its XCTest driver. The `test_e2e_ios_rntester` jobs on this PR verify the change.

Reviewed By: javache

Differential Revision: D127135564

Pulled By: cipolleschi

fbshipit-source-id: 675aba648bf343358aeea9cbdd359d8b5eb3b56f

Author: cipolleschi

packages/rn-tester/.maestro/sectionlist-viewability.yml

@@ -28,14 +28,16 @@ appId: ${APP_ID} # iOS: com.meta.RNTester.localDevelopment | Android: com.facebo
     visible:
       id: 'section-list-viewability-horizontal-wait'
     timeout: 30000
+# Target the second-to-last item: the last one can never reach the center, so
+# `centerElement` would burn extra swipes at the end of the list.
 - scrollUntilVisible:
     element:
-      id: 'Brownie'
+      id: 'Cheesecake'
     direction: RIGHT
     speed: 60
     visibilityPercentage: 50
     centerElement: true
-    timeout: 60000
+    timeout: 120000
 - extendedWaitUntil:
     visible:
       id: 'output'