mathlib3

6397e144 - feat(data/nat/cast): add nat.bin_cast for faster casting (#5664)

feat(data/nat/cast): add nat.bin_cast for faster casting (#5664) [As suggested](https://github.com/leanprover-community/mathlib/pull/5462#discussion_r553226279) by @gebner. Co-authored-by: Yakov Pechersky <pechersky@users.noreply.github.com>