[Metadata] Create Metadata Size Validator

[Eniola3321]

Description

Ensure metadata stays within configured storage limits.

Acceptance Criteria
Validate JSON size
Reject oversized metadata
Add tests

[ReinaMaze]

@ReinaMaze has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Gm maintainer can I work on this issue
ETA : 48 hours

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

[drips-wave]

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

🧑‍💻 @ReinaMaze: 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 🌊