[Contracts] Implement Notification Metadata Integrity Verification

[Abd-Standard]

Description

Introduce metadata integrity validation to prevent tampering with notification records.

Tasks
Add metadata hashing.
Store integrity proofs.
Create verification functions.
Add contract tests.

Acceptance Criteria
Integrity checks validate correctly.
Tampered metadata fails verification.
Tests cover edge cases.

[Olajcodes]

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

Hi maintainer, I'd love to work on this. I have background experience with stuff like this.

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

[drips-wave]

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

🧑‍💻 @dev-chinasa: 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

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

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