Prepare for release-plz

[brainstorm]

After this comment from @tones111, I wanted to contribute with setting up a reliable crates.io release automation for this repository, it has worked wonders at my dayjob project.

Hope it helps for you too! Next steps would be to locally run cargo install release-plz, outside the avr-hal repository (to avoid clashes with edition2024) and then run release-plz init inside avr-hal's root, like so:

avr-hal % release-plz init
👋 This process will guide you in setting up release-plz in your GitHub repository, using `gh` (the GitHub CLI) to store the necessary tokens in your repository secrets.
👉 Paste your cargo registry token to store it in the GitHub actions repository secrets.
💡 You can create a crates.io token on https://crates.io/settings/tokens/new, specifying the following scopes: "publish-new" and "publish-update".
? Paste your secret: *******

There's plenty of guidance on the official page: https://release-plz.dev/