multiboot2-v0.21.0

Fixes various memory safety problems where Miri detected UB. Now, all unit tests run succesfully also with Miri. So, the crate is now guaranteed
to be free of memory issues (if we can Trust Miri and the numerous unit tests 😁).

See CHANGELOG.md.

All PRs

• build(deps): bump cachix/install-nix-action from 26 to 27 by @dependabot in #217
• build(deps): bump bitflags from 2.5.0 to 2.6.0 by @dependabot in #219
• build(deps): bump crate-ci/typos from 1.21.0 to 1.22.9 by @dependabot in #218
• build(deps): bump crate-ci/typos from 1.22.9 to 1.23.6 by @dependabot in #221
• build(deps): bump derive_more from 0.99.17 to 0.99.18 by @dependabot in #222
• cargo: update all dependencies by @phip1611 in #223
• Refactoring by @phip1611 in #224
• multiboot2: massive refactoring, removed UB, Miri passes all tests by @phip1611 in #226

Full Changelog (git): multiboot2-v0.20.2...multiboot2-v0.21.0