Decorate unsafe code block with allow unused_unsafe

[z-tech]

Description

The CI has started giving an error that the unsafe block is not needed. However, the unsafe block cannot be removed and thus needs to be decorated with allow unused_unsafe.

closes: #1060

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• Wrote unit tests
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[Pratyush]

In which versions of Rust does this error happened.

[z-tech]

In which versions of Rust does this error happened.

nightly-x86_64-unknown-linux-gnu installed - rustc 1.93.0-nightly (6647be936 2025-11-09)

[weikengchen]

I feel that we just need to keep a note somewhere to remove this unused_unsafe when our target version (rust-version in cargo, currently 1.75) gets to 1.93.0 one day.