chore: address paste advisory (RUSTSEC-2024-0436)

[dobby-coder]

Closes #30.

Swap unmaintained paste dev-dep for its drop-in successor pastey (addresses RUSTSEC-2024-0436). Used only by benches/main.rs. Tests pass, fmt clean.

Reviewer quickstart

git fetch origin && git checkout chore/paste-advisory && cargo test --all-features

[dobby-coder]

Rule-compliance pass: trimmed the PR body to comply with no-justification-paragraphs-for-simple-changes — the original Summary / Changes / Verification sections narrated a 2-line dev-dep swap. Kept the closing keyword, a one-line summary, and the reviewer quickstart one-liner. No code changes.

[dobby-coder]

LGTM (cannot self-approve since the bot opened this PR).

Clean dev-dep swap: paste → pastey (drop-in fork). Only call site is the paste! macro in benches/main.rs:2, which pastey re-exports with identical syntax. Verified benches compile (cargo bench --no-run --all-features) and all CI is green (tests on linux/mac/windows, clippy, no-std wasm32). Addresses RUSTSEC-2024-0436 with zero production-code impact.

Ready for human approval and merge.