fix: use `expect` attributes instead of `allow`

[samueltardieu]

Requires MSRV to be bumped to 1.81.0.

[codspeed-hq[bot]]

CodSpeed Performance Report

Merging #608 will not alter performance

_{Comparing push-ozxuvrzpozlu (98c94c8) with main (1628bd2)}

Summary

✅ 36 untouched benchmarks