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## Description

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## Checklist

- [ ] `cargo fmt --check` produces no changes
- [ ] `cargo clippy --all-targets --all-features -- -D warnings` is clean
- [ ] `cargo clippy --no-default-features -- -D warnings` is clean (no_std)
- [ ] `cargo test` passes
- [ ] Added or updated tests (golden vectors for codec changes)
- [ ] Updated `CHANGELOG.md` for user-visible changes
- [ ] Commits are SSH/GPG-signed and signed-off (`git commit -s`, DCO)
