enh(UI): Removed month review card from stats page

[Wuyika]

Description

• Removed the month review card stats screen

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore

[sourceant]

Code Review Summary

This PR removes the 'Month in Review' card and its associated data processing logic from the StatisticsScreen. This is a UI simplification change that also cleans up unused imports and helper methods.

🚀 Key Improvements

• Reduced widget tree complexity in lib/presentation/statistics/statistics_screen.dart.
• Improved performance by removing the _buildSparkline transaction processing loop.
• Removed unused imports related to MonthInReview.

💡 Minor Suggestions

• Ensure that the files month_in_review_data.dart, month_in_review_screen.dart, and month_in_review_card.dart are also deleted from the project if they are no longer used anywhere else, to keep the codebase clean.

[sourceant]

Review complete. No specific code suggestions were generated. See the overview comment for a summary.