feat(io): implement Read, ReadReady, BufRead, Write, and WriteReady for VecDeque<u8>

[mkroening]

This PR implements both sync and async versions of Read, BufRead, and Write, as well as ReadReady and WriteReady for VecDeque<u8> by adapting the corresponding implementations from std.

[chrysn]

Generally I think it's good to have those provided, and the code does that.

The commits look a bit messy – was the intention to split them up between the sync and the async part?

The code looks good to me; several comments, but some are more for documenting that a part was checked (just mark them as resolved if you don't want to add anything). Those where I do suggest changes are all minor, so feel free to change things or not.

(Also, I'm just a guest contributor here, just trying to make it easier to get this merged).

[chrysn]

This looks like it's more code than the read above combined with the provided read_exactly – is there really a point to spelling this out over letting the compiler assemble the provided one?

[mkroening]

Apparently, yes. I did not reevaluate this code coming from std, but it was a conscious decision to specialize it: rust-lang/rust#132039

[chrysn]

It's pretty verbatim in places. I think that's fine given that both are licensed under "MIT OR Apache-2.0", and the original files do not have any copyright notes that point out concrete contributors (so the embedded-hal copyright notice should already cover that).

[chrysn]

This is redundant with the provided method.

[mkroening]

Yeah, I am aware of that. This is how I discovered the mismatch in requirements that's being discussed in #696.

I am happy to remove this if the maintainers are okay with moving forward with this PR before deciding on #696.

[mkroening]

Thanks for the external review! :)

The commits look a bit messy – was the intention to split them up between the sync and the async part?

No, the intention was to separate concerns:

1. Raise the embedde-io-async MSRV as required by the changes and implied through depending on embedded-io anyhow.
2. Implement I/O traits by adapting code from std.
3. Implement additional traits that are not present in std.

[chrysn]

Thanks; then all is fine with me.