Add doc-comments to all ContractError variants explaining when each is returned

[Kingsman-99]

Description

ContractError has 63 variants but many have no or only partial documentation explaining which entry point returns them and under what condition. Contributors adding new features need clear documentation to understand which error to use, and users need documentation to handle errors correctly.

Acceptance Criteria

• Every ContractError variant has at least one sentence of doc-comment
• Doc-comment names the entry point(s) that can return the error
• Doc-comment describes the specific condition that triggers the error
• All existing doc-comments are reviewed and updated if incomplete
• cargo doc --no-deps completes without warnings in contracts/split

Context

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

[gabrielujelistic-collab]

@gabrielujelistic-collab 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 @gabrielujelistic-collab to this issue.

[Akintobidavid]

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

I’ve reviewed the issue and can document all 63 ContractError variants with their entry points and triggering conditions, while reviewing existing comments for completeness. I’ll verify cargo doc --no-deps completes without warnings.

Please assign this to me, you won’t be disappointed, thank you.

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

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

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

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