feat(game): add scoreboard system with live and final score display

[PresenceOP-Coder]

Description

This pull request adds a scoreboard feature to the Flutter Flappy Bird game.
It introduces real-time score tracking and display during gameplay.
Changes include:

• Live score display during gameplay
• Automatic scoring when the bird successfully passes barriers
• Final score shown on the game over dialog
• Score reset when the player restarts the game

Semver Changes

• Patch (bug fix, no new features)
• Minor (new features, no breaking changes)
• Major (breaking changes)

Issues

Closes #6

Checklist

• I have read the Contributing Guidelines.

[PresenceOP-Coder]

@ashutosh-7503 plz add important labels and the last pr that i submitted (barrier logic one )has issue in scoring(you labels it medium instead of hard ) .