Clarify zero-multiple handling in jf-utils padding helpers

[daixihegu]

closes: #XXXX

This PR:

This PR clarifies the behavior of jf-utils padding helpers when they are called with a zero multiple.

Previously, compute_len_to_next_multiple(_, 0) panicked with Rust's modulo-by-zero message. This change adds an explicit assertion so callers get a clearer panic message, and documents the panic behavior for both compute_len_to_next_multiple and pad_with_zeros.

This PR does not:

Key places to review:

• cargo fmt -- --check
• cargo test -p jf-utils
• cargo clippy -p jf-utils --all-targets -- -D warnings
• git diff --check

---

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• Targeted PR against correct branch (main)
• Linked to GitHub issue with discussion and accepted design OR have an explanation in the PR that describes this work.
• Wrote unit tests
• Updated relevant documentation in the code
• Added relevant changelog entries to the CHANGELOG.md of touched crates.
• Re-reviewed Files changed in the GitHub PR explorer

[CLAassistant]

All committers have signed the CLA.

[gemini-code-assist]

Code Review

This pull request documents and clarifies the panic behavior of the padding helper functions when called with a zero multiple. Specifically, it adds an explicit assertion to compute_len_to_next_multiple to ensure multiple is non-zero, documents this behavior in the docstrings of both compute_len_to_next_multiple and pad_with_zeros, adds corresponding unit tests, and updates the CHANGELOG. There are no review comments, so we have no feedback to provide.

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[daixihegu]

@mrain @philippecamacho @akonring Hi, Could you please review this PR at your convenience? Thank you very much.