Add `no_std` support

[CrazyboyQCD]

[MarijnS95]

Almost forgot to mention: can you please drop the chore: prefix from your commit messages? It's not used by this project and does not have any meaning in this context.

a routine task, especially a household one.

I don't think a one-off no_std conversion in a crate is considered a "routine task" :slightly_smiling_face:

[CrazyboyQCD]

msrv is required to bump to either 1.75+(if we switch from thiserror to derive_more) or 1.81+ to get CI work.

[MarijnS95]

I'm thinking of raising the MSRV unconditionally, that seems a lot less tricky to users than pretending it's 1.71, as long as they turn on the "std" feature 😅

[MarijnS95]

I've squashed everything down into a single commit because our branch protection requires every individual commit to have been signed. Even if squash-merging will squash and resign the entire PR with GitHub's "web workflow" signature anyway 🤷

Since I contributed to and approve the final result, it makes sense for me to sign such a final result (but not individual commits) :)

[Jasper-Bekkers]

Should we go ahead and merge this?