RUSTSEC-2026-0105: core2 is unmaintained, all versions yanked

[github-actions]

Details
Package	core2
Version	0.4.0
Warning	unmaintained
URL	https://hachyderm.io/@piecritic/116404790999620656
Patched Versions	n/a

The maintainer decided stop maintaining crate and yanked all published versions.

Potential alternatives:

• embedded-io solves the same general problem
• no-std-io2 is a maintained fork