Update async-io requirement from 1.9.0 to 2.1.0

Updates the requirements on [async-io](https://github.com/smol-rs/async-io) to permit the latest version.
- [Release notes](https://github.com/smol-rs/async-io/releases)
- [Changelog](https://github.com/smol-rs/async-io/blob/master/CHANGELOG.md)
- [Commits](smol-rs/async-io@v1.9.0...v1.13.0)

---
updated-dependencies:
- dependency-name: async-io
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

raw/Cargo.toml

@@ -23,4 +23,4 @@ version = "0.1.0"
 femme = { workspace = true } 
 clap = { workspace = true }
 mio-serial = "5.0"
-async-io = "1.9.0"
+async-io = "2.1.0"