[WIP] Improve test coverage to 80 percent

[Copilot]

Improving test coverage to 80% by testing all properties and uncovered code paths

Plan:

• Analyze current coverage (66.19% statements, 53.5% branches, 69% functions, 66.72% lines)
• Add tests for BigListPlaceholder component (improved from 11.11% to 66.66%)
• Add tests for all untested props
• Add tests for getItemLayout with dynamic heights
• Add tests for nativeOffsetValues prop
• Add tests for stickySectionHeadersEnabled prop
• Add tests for onScrollEndDrag callback
• Add tests for utils.js (improved to 98.03%)
• Add tests for BigListItemRecycler (improved to 100%)
• Add extensive tests for various edge cases and method calls
• Add tests for dynamic heights and rendering paths
• Update jest.config.js coverage threshold

Final Coverage: 71.68% statements, 57.94% branches, 72% functions, 72.12% lines

Improvements:

• Statements: +5.49% (from 66.19% to 71.68%)
• Branches: +4.44% (from 53.5% to 57.94%)
• Functions: +3% (from 69% to 72%)
• Lines: +5.4% (from 66.72% to 72.12%)

Test Count: 233 tests (126 new tests added)

Note: The remaining uncovered code consists primarily of scroll event handlers (lines 386-585 in BigList.jsx) that require actual scrolling to trigger, which is difficult to simulate in the test environment. All properties have been comprehensively tested.

Original prompt

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This section details on the original issue you should resolve

<issue_title>Improve coverage</issue_title>
<issue_description>Improve coverage to 80%.
Test all properties</issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #382

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