Fix billion suffix logic to handle all positions >= 3 consistently

[Copilot]

The billion suffix generation used inconsistent code paths: position 3 fell through to a hardcoded return, while positions >= 6 used a formula-based approach. This made the logic harder to reason about and violated the principle of uniform handling.

Changes

• Unified billion handling: Changed condition from positionFromRight >= 6 to positionFromRight >= 3, so all billion positions use Math.floor(positionFromRight / 3) to calculate repetitions
• Constructor consistency: Replaced Array() with new Array() per project conventions

// Before: position 3 bypassed the formula
if (positionFromRight >= 6 && hasTrailingZeros) {
  const billionCount = Math.floor(positionFromRight / 3)
  return ' ' + Array(billionCount).fill('tỷ').join(' ')
}
return ' tỷ'  // position 3 hit this

// After: all positions use the same formula
if (positionFromRight >= 3 && hasTrailingZeros) {
  const billionCount = Math.floor(positionFromRight / 3)
  return ' ' + new Array(billionCount).fill('tỷ').join(' ')
}
return ' tỷ'  // only for non-trailing-zero cases

The behavior is unchanged (position 3 still produces ' tỷ'), but the implementation is now consistent across all billion positions.

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Copilot]

Pull Request Overview

This PR fixes a logic issue in the billion suffix generation for Vietnamese number reading and improves code consistency. The change corrects the condition for when to apply the repeated "tỷ" suffix pattern.

• Fixed the condition threshold from >= 6 to >= 3 for generating repeated billion suffixes
• Updated array instantiation to use new Array() for consistency

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