Add VStack renderable item culling tests

[honghaoz]

Motivation

• Verify VStack/VerticalStackNode correctly culls children outside the visible bounds and still includes children that are visible due to an offset.

Description

• Added two unit tests to Tests/ComposeUITests/ComposeNodes/VerticalStackNodeTests.swift: test_renderableItems_filtersOffscreenChildren and test_renderableItems_includesOffsetChildren that exercise renderableItems(in:) behavior with LayerNode children.
• Each test calls layout(containerSize:context:) on a VStack with fixed child frames and then asserts the frames returned by renderableItems(in:) match the expected visible items.

Testing

• No automated tests were executed as part of this change; the new unit tests were added but not run.

---

Codex Task

---

Note

Adds targeted coverage for VStack visibility culling in renderableItems(in:).

• Adds test_renderableItems_filtersOffscreenChildren and test_renderableItems_includesOffsetChildren in Tests/ComposeUITests/ComposeNodes/VerticalStackNodeTests.swift
• Verifies renderableItems(in:) returns only visible LayerNode items, culling offscreen children and including children visible due to .offset(...)

^{Written by Cursor Bugbot for commit a5d13e9. This will update automatically on new commits. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.74%. Comparing base (e864f3d) to head (a5d13e9).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master       #2   +/-   ##
=======================================
  Coverage   88.74%   88.74%           
=======================================
  Files          90       90           
  Lines        4346     4346           
=======================================
  Hits         3857     3857           
  Misses        489      489           

Flag	Coverage Δ
ComposeUI	88.74% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.