Optimize Array.prototype.push and pop with dense fast paths #5281

[dhruveshmishra]

This PR introduces fast-path optimizations for Array.prototype.pop and Array.prototype.push when operating on dense arrays.

Closes #5281

Currently, push and pop operations go through generic property access, which introduces unnecessary overhead. Since most arrays are dense, we can directly operate on underlying storage.

Implementation

• Added fast path using dense_indexed_properties_mut()
• Used direct vec.pop() and vec.push() for performance
• Ensured correctness by checking vec.len() == length
• Proper borrow handling using drop(obj)
• Fallback to existing logic for edge cases

Testing

• All tests pass (cargo test)
• No regressions observed

Notes

Optimization is applied conservatively to maintain correctness.