Implement dav1d-rs's Rust API

[leo030303]

I've copy pasted the PR from #1362 and updated it with some of the suggestions made on that pull request. The main changes are:

• Have all the public-facing Rust API code in its own file.
• Used some enums from rav1d instead of redefining new ones, and added in doc comments from the original dav1d-rs library to a few items.
• Removed as much unsafe code as I could and replaced it with the Rust methods from rav1d as much as possible.

It currently works as a drop-in replacement for dav1d-rs; adding in use rav1d as dav1d; to my fork of image makes everything work fine.

The only functional changes I made are I removed the unsafe impls of Send and Sync for InnerPicture so Picture is no longer Sync or Send. I looked through the code and I don't believe DisjointMut<Rav1dPictureDataComponentInner>, which is a field of one of its children, is thread safe, though I'm open to correction there; I'm pretty unfamiliar with unsafe Rust.

I also don't have safety comments on the two unsafe blocks in rust_api.rs; I'm unsure what these would look like, so open to suggestions there. These are mostly taken verbatim from the old pull request.

• Closes Provide Rust API #1252.

[kkysen]

Thanks for the much safer implementation! I'm still taking a closer look at the unsafes, as the few remaining are still quite critical, but I wanted to give some initial feedback in general first.

[kkysen]

@leo030303, could you rebase this on main? There are a lot of other commits in here now, so it's harder to review.

[leo030303]

I think the core of this PR, the rust API, seems to be in a good place, for the work aligning the implementation closer to the spec I think it makes sense to do those under separate PR's, but overall I think the rust API should be good to merge if it all looks fine from your end

[leo030303]

I think this was closed accidentally?
@kkysen

[kkysen]

I think this was closed accidentally? @kkysen

Oh, whoops, I didn't realize "fix" expressions for a PR comment close them. I thought it only worked on issues.

[Shnatsel]

Is there anything blocking this? I'd love to see this merged and published so we could drop the last remaining C library, dav1d, from the image crate.

[leo030303]

Is there anything stopping this from being merged? Happy to make any requested changes @kkysen

[leo030303]

The pipeline fails are in a file unrelated to this PR from what I can see

[leo030303]

@kkysen I think this should be ready for merging, assuming the one remaining unsafe block is okay, it looks fine to me with the extra checks added in, its following the safety suggestion in the slice::from_raw_parts docstring

[narodnik]

    pub fn send_data<T: AsRef<[u8]> + Send + Sync + 'static>(
        &mut self,
        buf: T,
        offset: Option<i64>,
        timestamp: Option<i64>,
        duration: Option<i64>,
    ) -> Result<(), Rav1dError> {
        assert!(
            self.pending_data.is_none(),
            "Have pending data that needs to be handled first"
        );

        let buf = buf.as_ref().to_vec().into_boxed_slice();

Why is buf marked as 'static? It doesnt need it since you copy it immediately with .to_vec(). I have a non-static &[u8] and have to copy it with .to_vec() just to pass it in and then you immediately copy it again.