Add overflow protection for score calculations

[Samuel1-ona]

Ensure score calculations (points * difficulty * weight * bonus) cannot overflow.

Acceptance Criteria:

• Use checked arithmetic for all score math
• Define maximum possible score
• Return error on overflow instead of panic
• Add test cases for edge values

[jaynomyaro]

@jaynomyaro has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi! I came across this issue and would love to work on it. I have experience with similar tasks and I'm confident I can investigate, implement a clean solution, and thoroughly test it before submitting a PR. If the issue is still open, I would appreciate it if you could assign it to me. Thank you!

ℹ️ Repo Maintainers: To accept this application, review their application or assign @jaynomyaro to this issue.

[Oluwasuyi-Oluwatimilehin-Daniel]

@Oluwasuyi-Timilehin has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hello maintainers I'm a full stack developer experience in building scalable systems I can handle this perfectly if assigned

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Oluwasuyi-Timilehin to this issue.

[drips-wave]

Congratulations, @jaynomyaro! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on June 30, 2026.

🧑‍💻 @jaynomyaro: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

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