Add `///` doc comment to `StorageKey` enum explaining the 50-variant Soroban limit

[Kingsman-99]

Description

contracts/split/src/storage_keys.rs has a module-level comment explaining the four-enum split, but StorageKey itself lacks a /// doc comment. New contributors editing the enum may not understand why it can have at most 50 variants. A /// doc comment on the enum itself reinforces this constraint.

Acceptance Criteria

• Add a /// doc comment to pub enum StorageKey explaining the 50-variant Soroban limit and that new keys should be appended (never reordered)
• cargo doc builds without warnings
• cargo test passes

Context

• Target file: contracts/split/src/storage_keys.rs

[olutundee]

@olutundee has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi Maintainer, I went through the issue and I'm clear on what's needed here. Happy to take this on and get you a solution that lines up with the acceptance criteria, feel free to assign it to me.

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

[sadiquhammedabubakar-art]

@sadiquhammedabubakar-art has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

Hi maintainer, I’d like to work on this issue. I’ll add a clear "///" doc comment to the "StorageKey" enum explaining Soroban’s 50-variant limit and why the enum is structured around it.

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

[lonerthefirst3-sudo]

@lonerthefirst3-sudo has applied to work on this issue as part of the Stellar Wave Program's 8th wave.

i would love to work on this

ℹ️ Repo Maintainers: To accept this application, review their application or assign @lonerthefirst3-sudo to this issue.

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Congratulations, @lonerthefirst3-sudo! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on August 31, 2026.

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[drips-wave]

This issue has been completed by @lonerthefirst3-sudo as part of the Stellar Wave Program's 8th Wave 🥳

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