Add `# Errors` section to `assert_unique_recipients` and `assert_recipients_have_trustlines`

[Kingsman-99]

Description

assert_unique_recipients and assert_recipients_have_trustlines in contracts/split/src/validation.rs lack # Errors doc sections. Without them, callers cannot tell from docs alone what error variant is returned in the failure path.

Acceptance Criteria

• Add /// # Errors\n/// Returns [ContractError::DuplicateRecipient] when a duplicate is found. to assert_unique_recipients
• Add /// # Errors\n/// Returns [ContractError::RecipientMissingTrustline] when a balance call fails. to assert_recipients_have_trustlines
• cargo doc --no-deps succeeds without warnings
• cargo test passes

Context

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

[Kenisank]

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Hello Maintainer, Please I would like to work on this issue

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[Peaostrel]

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i can handle this quickly

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[dollfins]

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hello maintainer, can i work on this issue

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[payfoxX]

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I love to fix this issue, kindly assign it to me. Thanks

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[Muyideen-js]

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Hi, I can fix this

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[Dankiddo]

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i would like to work on this project

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

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