Add input sanitization for user-provided strings

[ISTIFANUS-N]

Description

User-provided string inputs are not properly sanitized.

Acceptance Criteria

• Add maximum length checks
• Implement character validation
• Trim whitespace
• Reject invalid characters

[Spagero763]

@Spagero763 has applied to work on this issue as part of the Stellar Wave Program's 4th wave.

i can work on the issue as a smart contract developer

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Spagero763 to this issue.

[drips-wave]

Congratulations, @Spagero763! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on April 29, 2026.

🧑‍💻 @Spagero763: 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.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[drips-wave]

This issue has been marked as completed by a Drips Wave moderator for @Spagero763 as part of the Stellar Wave Program's 4th Wave 🥳

Moderator's reason: [Auto-assessed] The PR #435 directly addresses all requirements of issue #260 by implementing string trimming, length validation, and character set checks in the validation.rs module. The PR has been open for more than 24 hours without maintainer objections and provides a high-quality, comprehensive solution that includes additional security enhancements.

😎 @Spagero763: You earned 200 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here.

🧑‍💻 Repo maintainers: How'd the contributor do? Leave a review to share your experience working with them.

ℹ️ Note: This issue was marked complete via moderation. Points were issued even though the GitHub issue remains open.