Add read/write implems for generic arrays

[xlambein]

Hey! Thanks for the great project :-)

I needed to (de)serialize arrays of structs that implement DekuRead/Write, so I went ahead and added those trait implementations. They also supersede the implementations for all the uX/iX/fX array/slices, so I removed those.

There's a bit of unsafe code to avoid doing unnecessary allocations.

[sharksforarms]

The reason for this is because of potential performance impacts of default'ing here? let mut slice: [$typ; N] = [<$typ>::default(); N];

[xlambein]

Using default() requires that T implements Default, which imo is an unnecessary restriction. To me the safe alternative would be to do:

let mut v = Vec::with_capacity(N);
let mut rest = input;
for i = 0..N {
    let (new_rest, value) = T::read(rest, ctx)?;
    v.push(value);
    rest = new_rest;
}
Ok((rest, v.try_into().unwrap()))

That makes a few unnecessary allocations and checks, which are avoided with the unsafe section. It doesn't seem very critical, so if you'd rather do that I think it's fine! :-)

[sharksforarms]

Hey @xlambein sorry this took so long, this PR looks good to me.

[sharksforarms]

Released in 0.12.4, thanks @xlambein and sorry for the delay

[xlambein]

Oh, I missed the previous comment. Thanks a lot for merging! And no worries about the delay, thanks for maintaining this project!

[sharksforarms]

i.r. to the use of unsafe, we could utilize this: rust-lang/rust#75644 once it's released!

[wcampbell0x2a]

Tracking issue: rust-lang/rust#89379